Question

One pipe can fill a tank with oil in 3 hours. A second smaller pipe can fill the same tank in 7 hours. If both pipes were used at the same time, how long would they take to fill the tank?

Answer 1

2.1 hour

Explanation:

GIVEN: One pipe can fill a tank with oil in
`3` hours. A second smaller pipe can fill the same tank in
`7` hours.

TO FIND: If both pipes were used at the same time, how long would they take to fill the tank.

SOLUTION:

Let
`x` be the time taken by both pipes together.

Let total capacity of tank be
`=t`

Total oil filled by first pipe in one hour
`=(t)/(3)`

Total oil filled by second pipe in one hour
`=(t)/(7)`

Total oil filled in one hour if both pipes are opened
`=(10t)/(21)`

Total time taken by both pipes open together
`x=(t)/((10t)/(21))`

`x=2.1` hour

Hence it would taken 2.1 hour if both pipes are opened together.

Answer 2

Answer: 2.1 hours.

Explanation:

Given , Time taken by the first pipe to fill a tank = 3 hours

Time taken by the second pipe to fill the tank = 7 hours

If both pipes were used at the same time, then the time taken (t) by both of them to fill the tank ( together) will be :-

`(1)/(t)=(1)/(3)+(1)/(7)\\\\\Rightarrow\ (1)/(t)=(3+7)/(3*7)\\\\\Rightarrow\ (1)/(t)=(10)/(21)\\\\\Rightarrow\ t=(21)/(10)\\\\\Rightarrow\ t=2.1`

Therefore, time taken to fill the tank = 2.1 hours.