Question

26.
5. A boy takes 4 h to cover certain distance along
the flow and takes 6 h to cover the same distance
opposite to flow. In how much time, he will cross
this distance in still water?
(1) 4.5 h
(2) 5 h
(3) 2.4 h
(4) 4.8 h
plz give explanation​

Answer 1

Answer:

4.8 hr

Explanation:

Let day Distance = D

Speed in still Water =  X  km/Hr

Speed of River = R km/Hr

Along the flow Speed =  X + R  km/hr

Time Taken = D/(X + R)  = 4

Against the flow Speed =  X - R  km/hr

Time Taken = D/(X - R)  = 6

=> (X+R)/(X - R)  = 6/4

=>  (X+R)/(X - R)  = 3/2

=> 2X + 2R = 3X - 3R

=> X = 5R

D/(5R + R) = 4

=> D = 24R

time to cross same distance in still water

D/X  = 24R/5R = 4.8 hr