A boat takes 120min less to travel 30km downstream than to travel the same distance upstream If the ...........

Quantitative Aptitude ( CCS) Boats and Streams

A boat takes 120min less to travel 30km downstream than to travel the same distance upstream.If the speed of the boat in still water is 8kmph then the speed of the stream is

2kmph

8kmph

3kmph

4kmph

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Explanation:

Speed of the stream = x
(30/8-x) – (30/8+x)= 120/60 = 2/1
30(8+x) – 30(8-x) = 2[64 – x2] 240+30x-240x+30x = 2[64 – x2] 60x = 128- 2x2
2x2+60x-128 = 0
x2+30x-64 = 0
(x+32)(x-2) = 0
X=2kmph