Question

A boat takes 90 min less to travel 36 miles downstream than to travel the same distance upstream. If the speed of the boat in still water is 10 m/h, the speed of the stream is

Options

• 2 m/h

• 2.5 m/h

• 3 m/h

• 4 m/h

Answer 1

2 m/h
Explanation:
Let the speed of the stream x m/h. Then,
speed downstream = (10 + x) m/h,
Speed upstream = (10 - x) m/h.

∴ `36/((10-x))-36/((10+x))=90/60`

⇒ 72x x 60 = 90(100 - x²)

⇒ x² + 48x - 100 = 0

⇒ (x + 50)(x - 2) = 0

∴ x = 2 m/h

 [∵ -ve value neglecting]