Question

A boat can go 15km upstream and return downstream in 4 hours. The speed of the boat is 8km/hr. Find the speed of the stream

Answer 1

Answer:

2km/h

Step-by-step explanation:

Let the speed of stream be "x",

Speed = Distance / Time,

Time = Distance / Speed

According to question,

Time taken going upstream + Time taken going downstream = 4 hours

$\frac{15}{8-x} + \frac{15}{8 + x} = 4$

$\frac{15(8+x)+15(8-x)}{(8+x)(8-x)} = 4$

$\frac{120 + 15x + 120 -15x}{64-x^2} = 4$

$\\240 = 4(64-x^2)$

$\\\\64-x^2=60$

$-x^2 = -4$

$x = \sqrt{4}$ or $-\sqrt{4}$

As speed can't be negative, x can't be -2

Therefore, speed of stream = 2km/h