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ব্যাংক নিয়োগ প্রস্তুতি ⎯ লং কোর্স

পরীক্ষাব্যাংক নিয়োগ প্রস্তুতি ⎯ লং কোর্সতারিখতারিখ অনির্ধারিতসময়45 minutes
মোট প্রশ্ন২৯
সিলেবাস
Math - 04 - Ratio & Proportion, Partnership, Allegation or Mixture
ঘনত্ব
উত্তর
উত্তরিতবর্তমানপুনরায় দেখুনঅসম্পূর্ণ

ব্যাংক নিয়োগ প্রস্তুতি ⎯ লং কোর্স

ব্যাংক নিয়োগ প্রস্তুতি ⎯ লং কোর্স · তারিখ অনির্ধারিত · ২৯ প্রশ্ন

.
Ratul and Sajib were classmates. Their earnings now are in the ratio 5:6. The ratio of their expenses is 7:9. Sajib saves Tk. 3,000 every month while Ratul saves Tk. 1000/- more than Somesh. Find the total earnings and expenses of each of them.
  1. ক) Ratul - 25000, 21000; Sajib - 30000, 27000
  2. খ) Ratul - 30000, 27000; Sajib - 36000, 32000
  3. গ) Ratul - 36000, 32000; Sajib - 30000, 27000
  4. ঘ) None of the above
ব্যাখ্যা

Income ratio = Ratul : Sajib = 5 : 6 = 5/6
Common factor helps in finding actual values easily
So, take 'A' as a common factor.
Income of Ratul = 5A; Income of Sajib = 6A
(Expenses of Ratul)/(Expenses of Sajib) = (Ratul Income - Ratul Saving)/(Sajib Income -Sajib Saving) = 7/9
Since Ratul save, Tk. 1000/- more than Sajib, Ratul's savings = Tk. 4000/-
5A - 4000/6A - 3000 = 7/9
∴ 9(5A-4000) = 7(6A-3000)
∴ A = 5000
Income of Ratul = 5A = 25000 ; Income of Sajib = 6A = 30000
Spending of Ratul =25000 - 4000 = 21000
Spending of Sajib = 30000 - 3000 = 27000.

.
a : b = 3 : 4 and b : c = 9 : 7. What is a : b : c?
  1. ক) 3 : 13 : 7
  2. খ) 3 : 36 : 28
  3. গ) 27 : 16 : 28
  4. ঘ) 27 : 36 : 28
ব্যাখ্যা

B is common to both the ratios.
Values of b = 4 and 9 (That means they are not the same)
Make the values of 'b' the same as follows -
Multiply 3 : 4 up and down with 9 as shown
∴ (3 × 9)/(4 × 9) = 27/36 = a/b
Multiply 9 : 7 up and down with 4 as shown
∴ (9 × 4)/(7 × 4) = 36/28 = b/c
Since values of b are the same = 36
a : b : c = 27 : 36 : 28

.
Rimon saves Tk. 3395 from his salary. He needs to pay this money as a milk bill, electricity bill and mobile phone bill in the ratio 42 : 32 : 23. Find the money to be paid for each bill.
  1. ক) Tk. 1245, Tk. 1150 and Tk 1000
  2. খ) Tk. 1470, Tk. 1120 and Tk. 805
  3. গ) Tk. 1550, Tk. 1235 and Tk. 610
  4. ঘ) Tk. 1764, Tk. 1022 and Tk. 529
ব্যাখ্যা

Common factor helps in finding actual values easily
So, take 'A' as a common factor.
∴ 3 numbers will now be 42A, 32A and 23A
∴ 42A + 32A + 23 A = 3395
∴ 97A = 3395
∴ A = 35
3 parts of 3395 are
42A = 42 x 35 = 1470;
⇒ 32A = 32 x 35 = 1120
⇒ 23A = 23 x 35 = 805
These are the amounts to be paid.

.
Raju and Saju were carrying some money such that their money was in the ratio 3 : 8. A friend gives each of them Tk. 5 and their money is now in the ratio 2 : 5. Which is the smaller money of the two?
  1. ক) 45
  2. খ) 64
  3. গ) 105
  4. ঘ) 120
ব্যাখ্যা

The ratio of original money numbers = 3:8
Common factor helps in finding actual values easily
So, take 'M' as a common factor.
∴ Original numbers will be 3M and 8M
Adding 5 to them, we get (3M + 5) and (8M+5)
∴ (3M + 5)/(8M + 5) = 2/5 ............ (Ratio of new numbers is 2:5)
∴ 15M + 25 = 16M + 10
∴ M = 15
Smaller money value is 3M = 3 x 15 = 45.

.
A mixture contains alcohol and water in the ratio 4 : 3. If 5 liters of water is added to the mixture, the ratio becomes 4: 5. Find the quantity of alcohol in the given mixture.
  1. ক) 10
  2. খ) 12
  3. গ) 15
  4. ঘ) 18
ব্যাখ্যা

Let the quantity of alcohol and water be 4x litres and 3x litres respectively
4x/(3x + 5) = 4/5
⇒ 20x = 4(3x + 5)
⇒ 8x = 20
⇒ x = 2.5
Quantity of alcohol = (4 x 2.5) litres = 10 litres.

.
Three numbers A, B and C are in the ratio of 12 : 15 : 25. If sum of these numbers is 312, ratio between the difference of B and A and the difference of C and B is –
  1. ক) 3 : 7
  2. খ) 10 : 3
  3. গ) 3 : 10
  4. ঘ) 7 : 3
ব্যাখ্যা

Let the number A, B and C be 12a , 15a and 25a respectively
Then from the question 12a + 15a + 25a = 312
⇒ 52a = 312
⇒ a = 312/52
⇒ a = 6
Required ratio = {(15 × 6) - (12 × 6)}/{(25 × 6) - (15 × 6)}
= 3/10
= 3 : 10.

.
Out of three positive numbers, the ratio of the first and the second numbers is 3 : 4 that of the second and the third numbers is 5 : 6 if the product of the second and the third numbers is 4320. What is the sum of three numbers?
  1. ক) 177
  2. খ) 165
  3. গ) 185
  4. ঘ) 160
ব্যাখ্যা

The ratio of 1st and 2nd numbers = 3 : 4
The ratio of 2nd and 3rd numbers = 5 : 6
Let,
the 2nd number = 5x, third number = 6x
Product of 2nd and 3rd numbers = 4320
5x × 6x = 4320
x2 = 144
x = 12
2nd number = 60, 3rd number = 72,
1st number = (60/4) × 3 = 45
Sum of three numbers = 60 + 72 + 45 = 177

.
Two numbers are in the ratio of 21 : 26. If 8 is added in each, the new numbers are in ratio of 5 : 6. Find the ratio of numbers, if 6 is subtracted from each number?
  1. ক) 19 : 25
  2. খ) 18 : 23
  3. গ) 9 : 16
  4. ঘ) 6 : 7
ব্যাখ্যা

Let the numbers be 21x and 26x.
⇒ (21x + 8)/(26x + 8) = 5/6
⇒ 6(21x + 8) = 5(26x + 8)
⇒ 126x + 48 = 130x + 40
⇒ x = 2.
So, the numbers will be 42 and 52.
If 6 is subtracted, then numbers will be 36 and 46.
Required ratio = 36 : 46.
i.e. 18 : 23.

.
If A varies directly as B and inversely as C and A = 6, when B = 2 and C= 3, what is the value of A when B = 8 and C = 6?
  1. ক) 6
  2. খ) 18
  3. গ) 12
  4. ঘ) 24
ব্যাখ্যা

Let the constant be x,
so putting the first scenario in equation
A = x × (B/C)
⇒ 6 = x × 2/3
⇒ 2x = 18
⇒ x = 9
We can find out A in the second scenario by putting the value of x as 9
A = 9 × 8/6
⇒ A = 12.

১০.
The income of Asim, Shakil and Riaz is in the ratio of 12 : 9 : 7 and their spendings are in the ratio 15 : 9 : 8. If Asim saves 25% of his income. What is the ratio of the savings of Asim, Shakil and Riaz?
  1. ক) 15 : 18 : 11
  2. খ) 5 : 8 : 7
  3. গ) 23 : 18 : 11
  4. ঘ) 25 : 16 : 13
ব্যাখ্যা

Income = Expenditure + Saving
Asim : 12x = 15y + 3x (3x = 25% of 12x)
Shakil : 9x = 9y + (9x – 9y)
Riaz : 7x = 8y + (7x – 8y)
Therefore, 12x – 3x = 15y
x/y = 5/3
y = 3x/5
Therefore, savings = (income – expenditure)
Asim = 12x – 9x = 3x
Shakil = 9x - 9y = 9x - (27x/5)
= 18x/5
Riaz = 7x - 8y = 7x - (24x/5)
= 11x/5
i.e., the ratio of savings of Asim : Shakil : Riaz
= 3x : 18x/5 : 11x/5
= 15 : 18 : 11.

১১.
Robi invests Tk. 40,000/- in a car wash center and starts a business. After 4 months, Rasel joins the business with an investment of Tk.50,000. At the end of the year, they make a profit of Tk. 1,87,000/-. What will be Rasel's share in this profit?
  1. ক) Tk. 38800
  2. খ) Tk. 64666.67
  3. গ) Tk. 85000
  4. ঘ) Tk. 97000
ব্যাখ্যা

We know,
The ratio of Investment x Time = Ratio of Profit
∴ (A's investment x Time) : (B's investment x Time) = Profit of A : Profit of B

∴ (Robi's Investment x Time) : (Rasel's Investment x Time) = Robi's Profit : Rasel's Profit
∴ 40000 x 12 : 50000 x 8 = Robi's Profit : Rasel's Profit
∴ Robi's Profit : Rasel's Profit = 4,80,000 : 4,00,000 = 6:5
∴ Rasel's profit = (5/11) × 187000 = Tk. 85000

১২.
Three friends A, B and C invest in a business in the ratio 6 : 4: 10 respectively. They share the profit in the ratio 8 : 7 : 9 respectively. Find the ratio of time periods of their investment.
  1. ক) 3 : 2 : 5
  2. খ) 24 : 14 : 45
  3. গ) 80 : 75 : 54
  4. ঘ) 80 : 105 : 54
ব্যাখ্যা

We know that Ratio of Investment x Time = Ratio of Profit
∴ To find the ratio of time just divide respective profits ratios by respective investment ratios
So if the profit ratio is P1: P2 : P3 and the investment ratio is I1 : I2 : I3 then,
Time ratio is found by = (P1/I1) : (P2/I2) : (P3/I3)

6 : 4 : 10 can be reduced to 3 : 2 : 5. So, their investments are actually in the ratio 3 : 2 : 5.
The ratio of time periods for A, B, and C is found by = 8/3 : 7/2 : 9/5
Making denominators common by multiplying by 30
∴ The ratio of Time periods for A, B, and C = (30 × 8)/3 : (30 × 7)/2 : (30 × 9)/5
= 80 : 105 : 54

১৩.
A starts a flower shop with an investment Tk. 8000. After 3 months B joins him with an investment of Tk. 16000. C joins them later with an investment of Tk. 40,000/-. The business prospers and makes a profit of Tk. 1,12,000/- at the end of the year. If profits of A, B and C are in the ratio of 6 : 9 : 5, for how many months was C a part of the business?
  1. ক) 2 months
  2. খ) 3 months
  3. গ) 5 months
  4. ঘ) 6 months
ব্যাখ্যা

We know that
The ratio of Investment x Time = Ratio of Profit
∴ (A's investment × Time) : (B's investment × Time) = Profit of A : Profit of B

∴ Tk. 8000 × 12 months : Tk. 16000 × 9 months : Tk. 40000 × ? months = 6 : 9 : 5
∴ 96000 : 144000 : 40000 × ? = 6 : 9 : 5
By direct observation we can say, if common factor is K, then
6K = 96000;
∴ K = 16000;
and 5K = 40000 × ?
? = 5k/40000
= (5 × 16000)/40000
= 2 months.

১৪.
Two friends Roman and Shimul invest in a grocery shop. Shimul invests Tk. 25000/- while Roman invests Tk. 35000. Third friend Salim, joins them with the condition that all of them must get equal share of profit. To do so, he gives Tk. 400000 to Roman and Shimul to share between themselves. Find the ratio in which Roman and Shimul should share the money given by Salim?
  1. ক) 5:7
  2. খ) 7:5
  3. গ) 7:13
  4. ঘ) 13:7
ব্যাখ্যা

The total value of investment of Roman and Shimul after 12 months is =
Tk. 35000 x 12 months : Tk. 25000 x 12 months = 420000 : 300000

Profits need to be the same so investment share must be the same too.

Now 400000 given by Salim needs to be shared by Roman and Shimul so that their investment value becomes the same.
∴ If Tk. X must be given to Roman,
Then,
420000 + X = 300000 + (400000-X)
∴ X = Tk. 140000 = Roman should get this much
Required ratio = Share of Roman: Share of Shimul
= 140000 : (400000 - 140000)
= 7 : 13.

১৫.
B invested three-fourths of what C invested. A invested 20% more than B. What is C's investment, if total investment is Tk. 3816
  1. ক) Tk. 1300
  2. খ) Tk. 1440
  3. গ) Tk. 1650
  4. ঘ) Tk. 1800
ব্যাখ্যা

Let investment of C be Tk. 100
So the investment of B = Three-fourths of C = 3/4 of Tk. 100 = Tk. 75
Investment of A = 20% more than B = 20% more than Tk. 75 = Tk. 90
Ratio of investment of A, B, and C = 90 : 75 : 100 = 18 : 15 : 20
Investment of C = 20/(18 + 15 + 20) × 3816
= Tk. 1440.

১৬.
Armaan and Ghalib started a cafe with Tk. 40000 and Tk. 80000, respectively. Ghalib got married to someone in another town and left after 7 months. But Jishan immediately replaced him with an investment of Tk. 144000. At the end of the year, the business performed well and registered a profit of Tk. 50600.What is Ghalib’s share in this profit?
  1. ক) Tk. 13800
  2. খ) Tk. 16100
  3. গ) Tk. 16500
  4. ঘ) Tk. 16866.67
ব্যাখ্যা

We know,
The ratio of Investment x Time = Ratio of Profit
∴ (A's investment x Time) : (B's investment x Time) = Profit of A : Profit of B

The total value of investment of Arman, Ghalib, and Jishan after 12 months is =
Tk. 40000 x 12 months : Tk. 80000 x 7 months : Tk. 144000 x (12 - 7)months = 480000 : 560000 : 720000
∴ Profit ratio = 240000 : 280000 : 360000 = 6 : 7 : 9
∴ Share of Ghalib = 7/(6 + 7 + 9) x 50600 = Tk. 16100

১৭.
A and B started a business jointly A's investment was thrice the investment of B and the period of his investment was two times the period of investment of B. If B received Tk. 4000 as profit, then their total profit is :
  1. ক) Tk. 22000
  2. খ) Tk. 28000
  3. গ) Tk. 32000
  4. ঘ) Tk. 36000
ব্যাখ্যা

Suppose B invested Tk. x for y months.
Then, A invested Tk. 3x for 2y months.

So,
A : B = (3x × 2y) : (x × y)
= 6xy : xy
= 6 : 1.
B's profit : Total profit = 1 : 7.

Let the total profit be Tk. x
Then, 1/7 = 4000/x
⇒ x = Tk. 28000.

১৮.
Himu invested 10% more than Tushar. Tushar invested 10% less than Rubel. If the total sum of their investments is Tk. 5780, how much amount did Rubel invest ?
  1. ক) Tk. 2010
  2. খ) Tk. 2200
  3. গ) Tk. 2100
  4. ঘ) Tk. 2000
ব্যাখ্যা

Let money invested by Rubel = Tk. x
Money invested by Tushar = 9/10 x = 0.9x
Money invested by Himu = 9/10x × 110/100 = 0.99x
Also, x + 0.9x + 0.99x = 5780
= x= 5780/2.89
= 2000

Therefore, amount invested by Rubel is Tk. 2000.

১৯.
A's income is Tk. 140 more than B's income and C's income is Tk 80 more than D's. If the ratio of A's and C's income is 2 : 3 and the ratio of B's and D's income is 1 : 2, then the incomes of A, B, C and D are respectively
  1. ক) Tk. 60, Tk.120, Tk. 320 and Tk. 240
  2. খ) Tk.300, Tk.160, Tk. 600 and Tk. 520
  3. গ) Tk.400, Tk.260, Tk. 600 and Tk. 520
  4. ঘ) Tk.320, Tk.180, Tk. 480 and Tk. 360
ব্যাখ্যা

A : C = 2 : 3 or 2x : 3x
B : D = 1 : 2 or y : 2y
According to question,
2x - 140 = y .... (i)
3x - 80 = 2y .... (ii)

multiply equation (i) by 2 and solved
4x - 280 - 3x + 80 = 2y - 2y
⇒ x - 200 = 0
⇒ x = 200

Now put value of x in equation (i)
(2 × 200) - 140 = y
⇒ 400 - 140 = y
⇒ y = 260

A's salary = 2x = Tk. 400
B's salary = y = Tk. 260
C's salary = 3x = Tk. 600
D's Salary = 2y = Tk. 520

২০.
An 80L solution of alcohol and water has 45% alcohol in it. If you want the mixture to be 75% alcohol, how much alcohol would you add to it?
  1. ক) 30 litres
  2. খ) 75 litres
  3. গ) 96 litres
  4. ঘ) 110 litres
ব্যাখ্যা

Current alcohol quantity = {(45/100) × 80}
= 36 Litres.

Let A be alcohol added.
So, 36 + A = (75/100) × (80 + A)
⇒ 36 + A = (3/4) × (80 + A)
⇒ 144 + 4A = 240 + 3A
∴ A = 96 Litres =

96 Litres is the additional quantity of alcohol to be added.

২১.
A vessel contains 40 litres of orange juice. 4 litres of orange juice in the vessel was replaced by water. This process was again repeated twice with the mixture. How much orange juice is there in the final mix?
  1. ক) 28 litre
  2. খ) 29.16 litre
  3. গ) 32 litre
  4. ঘ) 32.29 litre
ব্যাখ্যা

First 4L orange juice was removed
So now in 40L mixture, there is 40 - 4 = 36 litres orange juice and 4 litres water
Now, remove 4L mixture. While doing this proportionate amount of juice and water gets removed.
Amount of juice removed = 4 × (Juice quantity/Mixture quantity)
= 4 × (36/40)
= 3.6 Litres.

Orange Juice remaining = 36-3.6 = 32.4 Litres
Again 4L mixture removed
Amount of juice removed = 4 × (Juice quantity/Mixture quantity)
= 4 × (32.4/40)
= 3.24 Litres.

Juice remaining = 32.4 - 3.24
= 29.16 Litres.

২২.
The drink for children has juice and water in the ratio 5:2 while the drink for adults has them in ratio 7:4. If both the mixes are poured in a jug, find the final ratio of water to juice in the jug.
  1. ক) 8:35
  2. খ) 25:52
  3. গ) 35:8
  4. ঘ) 52:25
ব্যাখ্যা

Children's drink → Juice : Water = 5 : 2 → Total 5 + 2 = 7 parts of liquid
Adult's drink → Juice : Water = 7 : 4 → Total 7 + 4 = 11 parts of liquid

Jug juice = Juice from children's mix + juice from adult mix = 5/7 + 7/11
= 104/77
Jug Water = Water from children's mix + Water from adult's mix = 2/7 + 4/11
= 50/77

Water to juice ratio in Jug = 50/77 : 104/77
= 50 : 104
= 25 : 52

২৩.
Three vessels contain a milk mixture 30 litre each. When put in a big vessel, they result in a mixture of milk and water in the ratio 2:1. If the ratio is to be reversed to make it 1: 2, how much more water should be added to the mix?
  1. ক) 20L
  2. খ) 40L
  3. গ) 90L
  4. ঘ) 100L
ব্যাখ্যা

3 vessels of 30 litres each = 3 X 30 = 90 ml milk mixture
Amount of milk in mixture = 2/(2 + 1) × 90 = 60L
Amount of water = 90 - 60 = 30L

To make milk to water ratio 1 : 2, we simply need to make water double of milk.
By direct observation,
we can say that we should have 60L x 2 = 120L water to make the required ratio

We already have 30L,
we need (120 - 30) = 90L more water.

২৪.
3 varieties of wheat were mixed at a warehouse. The rate of Type 1 wheat was Tk 145 Kg and the rate of Type 2 wheat was Tk. 20 per kg more than Type 1. The quantities of 3 varieties of wheat were in the ratio 2 : 1 : 3 respectively. The mix was finally sold at the rate of Tk. 180 per kg. Find the price of the 3rd type of wheat?
  1. ক) Tk. 196.58
  2. খ) Tk. 208.33
  3. গ) Tk. 210
  4. ঘ) Tk. 215.67
ব্যাখ্যা

Let the rate of 3rd type of wheat be Tk. W
Quantity ratio = 2 : 1 : 3
This means if we take 2kg of Type 1 and 1 kg of Type 2, then we must take 3kg of Type 3.
Also, the mix will have 2kg + 1kg + 3kg = 6 kg quantity.
∴ (145 x 2) + (165 x 1) + (3 x W) = 6 x 180
⇒ 290 + 165 + 3W = 1080
⇒ 3W = 1080 - 455
⇒ 3W = 625
⇒ W = 625/3
⇒ W = 208.33

∴ W = Tk. 208.33 per kg = 3rd type price per kg

২৫.
A can contains a mixture of two liquids A and B in the ratio 7 : 5. When 9 litres of mixture are drawn off and the can is filled with B, the ratio of A and B becomes 7 : 9. How many litres of liquid A was contained by the can initially?
  1. ক) 10
  2. খ) 20
  3. গ) 21
  4. ঘ) 25
ব্যাখ্যা

Suppose the can initially contains 7x and 5x litres of mixtures A and B respectively
Quantity of A in mixture left = {7x - (7/12) × 9} = 7x - 21/4
Quantity of B in mixture left = {5x - (5/12) × 9} = 5x - 15/4

According to the question,
(7x - 21/4)/{(5x - 15/4) + 9} = 7/9
⇒ (28x - 21)/(20x + 21) = 7/9
⇒ 252x - 189 = 140x + 147
⇒ 252x - 140x = 147 + 189
⇒ 112x = 336
⇒ x = 3.

So, they can contain 21 litres of A.

২৬.
A mixture of 150 liters of wine and water contains 20% water. How much more water should be added so that water becomes 25% of the new mixture?
  1. ক) 10 Litres
  2. খ) 20 Litres
  3. গ) 30 Litres
  4. ঘ) 40 Litres
ব্যাখ্যা

Number of liters of water in 125 liters of the mixture = 20% of 150
= 1/5 of 150
= 30 liters

Let us Assume that another 'P' litres of water is added to the mixture to make water 25% of the new mixture.
So, the total amount of water becomes (30 + P) and the total volume of the mixture becomes (150 + P).

Thus, (30 + P) = 25% of (150 + P)
⇒ 30 + P = 25/100 of (150 + P)
⇒ 30 + P = (1/4) × (150 + P)
⇒ 120 + 4P = 150 + P
⇒ 4P - P = 150 - 120
⇒ 3P = 30
⇒ P = 10

10 Litres of water is added to the mixture to make water 25% of the new mixture.

২৭.
4 kg of metal contains 1/5 copper and rest in Zinc. Another 5 kg of metal contains 1/6 copper and rest in Zinc.The ratio of Copper and Zinc into the mixture of these two metals:
  1. ক) 39 : 231
  2. খ) 49 : 221
  3. গ) 94 : 181
  4. ঘ) 36 : 272
ব্যাখ্যা

Copper in 4 kg = 4/5 kg and
Zinc in 4 kg = 4 x (4/5) kg

Copper in 5 kg = 5/6 kg and
Zinc in 5 kg = 5 x (5/6) kg

Therefore, Copper in mixture = (4/5) + (5/6) = 49/30 kg
and Zinc in the mixture = (16/5) + (25/6) = 221/30 kg

Therefore the required ratio = 49/30 : 221/30
= 49 : 221.

২৮.
A milkman claims to sell milk at its cost price, still, he is making a profit of 30% since he has mixed some amount of water in the milk. What is the % of milk in the mixture?
  1. ক) 71.02%
  2. খ) 76.92%
  3. গ) 63.22%
  4. ঘ) 86.42%
ব্যাখ্যা

Let the milk he bought is 1000 ml
Let C.P of 1000 ml is Tk. 100

Here let he is mixing K ml of water
He is getting 30% profit

⇒ Now, the selling price is also Tk. 100 for 1000 ml
⇒ 100 : K%
⇒ 100 : 30
10 : 3 is the ratio of milk to water

Percentage of milk = 10 x 100/13
= 1000/13
= 76.92%

২৯.
The amount of water (in ml) that should be added to reduce 9 ml lotion, containing 50% alcohol, to a lotion containing 30% alcohol is?
  1. ক) 6 ml
  2. খ) 11 ml
  3. গ) 15 ml
  4. ঘ) 9 ml
ব্যাখ্যা

Let us assume that the lotion has 50% alcohol and 50% water.
ratio = 1:1
As the total solution is 9ml
alcohol = water = 4.5ml
Now if we want the quantity of alcohol = 30%
The quantity of water = 70%
The new ratio = 3:7

Let x ml of water be added
We get,
4.5/(4.5 + x) = 3/7
⇒ 9/(9 + 2x) = 3/7
⇒ 63 = 27 + 6x
⇒ 6x = 63 - 27
⇒ 6x = 36
⇒ x = 6

Hence 6ml of water is added.