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

Answer: 2.1 hours.

Step-by-step 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 :-

$\dfrac{1}{t}=\dfrac{1}{3}+\dfrac{1}{7}\\\\\Rightarrow\ \dfrac{1}{t}=\dfrac{3+7}{3\times7}\\\\\Rightarrow\ \dfrac{1}{t}=\dfrac{10}{21}\\\\\Rightarrow\ t=\dfrac{21}{10}\\\\\Rightarrow\ t=2.1$

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

Answer 2

Answer:

2.1 hour

Step-by-step 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 $=\frac{t}{3}$

Total oil filled by second pipe in one hour $=\frac{t}{7}$

Total oil filled in one hour if both pipes are opened $=\frac{10t}{21}$

Total time taken by both pipes open together $x=\frac{t}{\frac{10t}{21}}$

$x=2.1$ hour

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