Question

Aboat covers 32 km upstream and 36 km downstream, in 7 hours Also it Covers
40 km upstream and 48 km downstream in 9 hours. Find the speed of boat in still
water and that of the stream
(CBSE)​

Answer 1

LET ‘V’ AND ‘v’ BE THE SPEED OF BOAT AND STREAM

DOWN STREAM SPEED = V + v

UP STREAM SPEED = V - v

CONDITION 1 : 32/((V-v) + 36/(V+v)=7 ; (i.e) 160/(V-v) + 180/(V+v) = 35

CONDITION 2 : 40/(V-v) + 48/(V+v) = 9 ;(i.e) 160/(V-v)+192/(V+v) = 36

HENCE 12/(V+v) = 1; (V+v) = 12

FROM CONDITION 1, 32/(V-v) + 36/12 = 7; (V-v) = 8

SOLVING ‘V’ = 10 AND ‘v’ = 2

SPEED OF THE BOAT IN STILL WATER = V = 10 km/hr

SPEED OF THE STREAM = v = 2 km/hr