(A) 3 Km/h
(B) 4 Km/h
(C) 6 Km/h
(D) 8 Km/h
Correct Option is: B
Let speed of the boat in still water be ‘x’ km/hr
Speed of the stream be ‘y’ km/hr
50 / (x –y) + 78 / (x +y) = 16 ———ïƒ 1
70 / (x –y) + 104 / (x +y) =22 ———ïƒ 2
By equation 1 * 7 and 2 * 5 we get,
350 / (x – y) + 546 / (x + Y) = 112
350 / (x – y) + 520 / (x + Y) = 110
Subtracting the above equation we get
26 / x + y = 2
x + y = 13 ——-ïƒ 3
substitute 3 in 1
50 / x – y = 10
x – y = 5 ———–ïƒ 4
solving 3 and 4 we get
2x = 18
x = 9 km/hr
y = 4 km/hr