Question

Two pipes can fill a tank in 20 minutes and 30 minutes respectively. If both the pipes are opened simultaneously then the tank will be finished in?

(a) 10 min

(b) 12 min

(c) 15 min

(d) 25 min

Answer 1

Let the first pipe be closed after x min.

Part filled by two pipes in x minutes = x(1/20+1/30)=5x/60=x/12

Part filled by the second pipe in (18−x)(18−x) = 18−x/30

x/12+18−x/30= 1

10x+72−4x=120

6x = 120 - 72 = 48

x = 8 minutes

hope this helps you out!

Answer 2

Answer:

1/20 +1/30

3+2 /60

1/12

Multiplicative inverse = 12

So they will do the work in 12 minutes.