a boat travel at a speed of 20 km/h in still water the current in a river flows at 5 km/h    so that downstream the boat can travel at 25 km/h and upstream it travels at only 15 km/h the boat has only enough fuel for 3 hours.after what time does the boat turn around so that it has enough fuel to return to base Let us say boat travel xkm distance from base in t1 hours down stream when it turn around and comes upstream.

`t1 = x/25`

For the return travel let us say it takes t2 hours.

`t2 = x/15`

How ever at the critical time limit;

`t1+t2 = 3`

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Let us say boat travel xkm distance from base in t1 hours down stream when it turn around and comes upstream.

`t1 = x/25`

For the return travel let us say it takes t2 hours.

`t2 = x/15`

How ever at the critical time limit;

`t1+t2 = 3`

`x/25+x/15 = 3`

`(x(3+5))/75 = 3`

`x = (75xx3)/8`

`x = 28.125`

`t1 = x/25 = 28.125/25 = 1.125`

So the boat should turn around in 1.125 hours to return to base without running out of fuel.

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