# math

A boat takes 90 minutes less to travel 36 km downstream then to travel the same distance upstream.If the speed of the boat in still water is 10 kmph.What is the speed of the current?

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1. since time = distance/speed,

36/(10+x) = 36/(10-x) - 3/2
x = 2

check:

36/12 = 3
36/8 = 4.5
ok

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posted by Steve
2. I don't understand the solve.please explain it.

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posted by sangita
3. If the current's speed is x, then
10+x is the downstream speed of the boat
10-x is the upstream speed.

the downstream time is 90 minutes (3/2 hours) less than the upstream time. Hence, the given equation.

36/(10+x) = 36/(10-x) - 3/2
36(10-x) = 36(10+x) - 3/2 (10-x)(10+x)
now just expand the factors and collect terms to get

x^2 + 48x - 100 = 0
(x+50)(x-2) = 0

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posted by Steve
4. Couldnt get thr ans sir pls solve it..

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posted by Aruna

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