Question

The Bubna dam has four inlets. Through the first three inlets, the dam can be filled in 12 minutes; through the second, the third and the fourth inlet, it can be filled in 15 minutes; and through the first and the first inlet, in 20 minutes. How much time will it take all the four inlets to fill up the dam?

विकल्प

• 8 min

• 10 min

• 12 min

• None of these

Answer 1

10 min

Explanation:

Let Pipes be A, B, C and D

`1/"A"+1/"B"+1/"C"=1/12`

`1/"B"+1/"C"+1/"D"=1/15`

`1/"A"+1/"D"=1/20`

Adding all equations

`2[1/"A"+1/"B"+1/"C"+1/"D"]=1/12+1/15+1/20=1/5`

`1/"A"+1/"B"+1/"C"+1/"D"=1/10` min

All the inlets together can fill in 10 min