Question 522921
Really problems like this are always fraction problems.
What we try to find is the fractions that are multiplied to do "1 whole job".
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The crew of 4 people can complete 3 walls in 36 minutes.
The crew can paint 1 wall in 1/3 * 36 = 12 minutes.
The crew does 1/12 of a wall per minute.
Each person is 1/4 of the crew, so each person does 1/4*1/12 = 1/48 of a wall per minute.
So, we know know that one person can do 1/48 of a wall per minute.
5 people can do 5*1/48 = 5/48 of a wall per minute.
So, in 48 minutes they can do 48 min * 5/48  wall/min = 5 walls.
To do 10 walls will take: 2 * 48 min = 96 min.
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We found that "1 whole wall" takes 12 minutes.
In turn, this means they can do 1/12 of the job per minute.
1/12 per minute * 12 minutes = 1 wall
A crew of 5 is 1.25 more than a crew of 4, so they can paint 25% faster per minute.
(5-4)/4 = 1/4 = .25
That means they can do 1 1/4 or 1.25 wall per 12 minutes.
Instead of 12 minutes per wall, they can do 1 wall in 12/1.25 = 9.6 min.
To do 10 walls will take 10*9.6 = 96 minutes.