Bank Math Master১টি পরীক্ষায় এসেছেপ্রশ্ন ৯The speed of a boat in still water is 9 km/h. The time it takes to travel downstream is half the time it takes to travel upstream. What is the speed of the stream?ক3 km/hখ2.5 km/hগ4 km/hঘ3.5 km/hউত্তর দেখুন