Question

A work crew has a new pump and an old pump. The new pump can fill a tank in 5 hours, and the old pump can fill the same tank in 7 hours. Write and solve an equation for the time it will take both pumps to fill one tank if the pumps are used together

Answer 1

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new pump rate::
`(1)/(5)` job/hr
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old pump rate::
`(1)/(7)` job/hr
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together rate::
`(1)/(x)` job/hr
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Equation:
rate + rate = together rate

`(1)/(5)` +
`(1)/(7)` =
`(1)/(x)`7x + 5x = 35
12x = 35
x =
`(35)/(12)` = 2
`(11)/(12)` hr = 2hr 55 min (time to do the job together)