Query Detail : RBI Assistant Prelims

a boat can cover a distance of 7.2km downstream and 3.2 km upstream in 2 hours. It can also cover 1.5 km downstream and 0.6 km upstream in 24 minutes. what is the speed of the boat when going downstream?
pooja,   January 29th 2020,  
RBI Assistant Prelims


Let Speed of downstream = x & that of upstream = y

So 7.2/x  + 3.2/y = 2 ---(1)

and 1.5/x + 0.6/y = 24/60   ---(2)

LCM of 7.2 and 1.5 = 36    So multiplying (1) by 5 and multiplying (2) by 24, we will get, 

 36/x + 16/y = 10    ---(3)

36/x + 14.4/y = 9.6   ---(4)

Subtracting (4) from (3), we will get,

1.6/y = 0.4

y = 4

and by putting value of y in (1), we will get x = 6

So Speed of boat in downstream = 6kmph