Question

Sally can paint a room in 5 hours while it takes Steve 8 hours to paint the same room. How long would it take them to paint the room if they worked​ together?

Answer 1

Answer: about 3 hours and 5 minutes

Explanation:

Sally can paint
`(1)/(5)` of the room in an hour while Steve is able to paint
`(1)/(8)` in an hour.

To find how long it would take to paint the room together you add the two fractions together:

`(1)/(5) + (1)/(8)`

To add or subtract fractions we find a common denominator and add the numenators:

`(1)/(5) = (8)/(40)`
`(1)/(8) = (5)/(40)`

`(5)/(40) + (8)/(40) = (13)/(40)`

The inverse of the fraction is hours per room =
`(40)/(13)`

`(40)/(13)` = 3.077 = about 3 hours and 5 minutes.

Answer 2

Sally does 1/5 of a room per hour.

Steve does 1/7 of a room per hour.

Together --> 1/5 + 1/7 = 12/35 rooms per hour.

The inverse is hours per room = 35/12

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Parallel work is similar to parallel flow and parallel resistors.

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PS 5*7/(5+7) = 35/12

Explanation: