Time & Work, Chain Rule

A takes thrice as long to do a piece of work, as B takes. A & B together can finish a piece of work in 15 days. A alone can do it in -

3 pumps working 8 hours a day, can empty a tank in 2 days. How many hours a day must 4 pumps work to empty the tank in 1 day?

Amir and Hannan working together can finish a work in 3 hours. If they work alone, Hannan takes 3 times as long as Amir. How long does Hannan take to finish the job alone?

A computer can perform 30 identical tasks in 6 hour. At that rate, what is the minimum number of computers that should be assigned to complete 80 of the tasks within 3 hours?

Running at the same constant rate, 6 identical machines can produce a total of 270 bottles per minute. At this rate, how many bottles could 10 such machines produce in 4 minutes?

50 persons can do a work in 12 day's by working 8 hours a day. Working how many hours per day can 60 persons finish the work in 16 days?

A, B and C working individually can complete a task in 30 days, 15 days and 10 days respectively. If A starts working alone and B and C helps A on every 2nd and 3rd day respectively, how long will it takes to be completed?

A map has a scale of 1 cm to 3 km, what length on actual ground does a 3 cm length on the map represent?

If Michael can shovel all the snow of a standard driveway in 12 minutes, and Emon can shovel all the snow of a standard driveway in 36 minutes, then working together, how many minutes would it take for them both to shovel all the snow of a standard driveway?

Three workers can do a job in 12 days. Two of the workers work twice as fast as the third. How long would it take one of the faster workers to do the job himself?

A is 30% more efficient than B. How much time will they, working together, take to complete a job which A alone could have done in 23 days?

A takes twice as much time as B or thrice as much time as C to finish a piece of work. Working together, they can finish the work in 2 days. B can do the work alone in:

Arif bought 17 pens of three colors- black, green and red. They cost Tk. 5, Tk. 10 and Tk. 25 each respectively. The total amount that Arif paid was Tk. 205. If Arif bought twice as many green pens as red pens, how many black pens did he buy?

A tap can fill a tank in 6 hours. After half the tank is filled, three more similar taps are opened. What is the total time taken to fill the tank completely?

X can do a piece of work in 20 days and Y can do the 1/7th of the same work in 5 days. In how many days together can they complete the 11/14th of the total work?

Mr. Rafin can complete a job in 15 days. while Mr. Shafin takes twice as long to do the same job. If they work together, how many days will they require to complete the job?

A 10% monthly salary increase resulted in a Tk. 9,000 per year increase in salary for an employee. What was has monthly salary before the increase? 

A car washer machine can wash 8 cars in 18 minutes. How many cars can be washed at the same rate in 3 hours?

A mechanic repairs 4 cars in 5/3 hours. How many cars can he repair in 50 minutes? 

A tap can fill a tank in 6hours. After half the tank is filled, three more similar taps are opened. What is the total time taken to fill the tank completely?