Question

One pipe can fill a tank in 4 hours. A second pipe also requires 4 hours, but a third

needs three hours. How long will it take to fill the tank if all three pipes are open?

Answer 1

1.2 hours

Explanation:

we need to see how much each pipes does in the same amount of time

The least common multiple of 3 hours and 4 hours is 12 hours

In 12 hours:

Pipe 1 at 4 hours to fill a tank fills 3 tanks

Pipe 2 at 4 hours to fill a tank fills 3 tanks

Pipe 3 at 3 hours to fill a tank fills 4 tanks

All three pipes can fill 10 tanks in 12 hours

12 hours/10 tanks = 1.2 hours to fill one tank

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Doing just the math

1/4 + 1/4 + 1/3 = x

3/12 + 3/12 + 4/12 = 10tanks/12 hours

12hours/10tanks = 1.2 hours

Answer 2

Explanation:

We will use the idea here that the first 2 pipes can get 1/4 of the job done in an hour, and that the third pipe can get 1/3 of the job done in an hour. We need to know then the number of hours it will take to fill the tank if all 3 work together. The equation looks like this:

`(1)/(4)+ (1)/(4)+ (1)/(3)= (1)/(x)` Now we find a common denominator and solve for x. The common denominator is 12x. Multiplying everything by 12 x gives us

3x + 3x + 4x = 12 and

10x = 12 so

x = 1.2 hours