SOLUTION: It takes 49 minutes for 4 people to paint 7 walls. How many minutes does it take 9 people to paint 9 walls?

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Question 941108: It takes 49 minutes for 4 people to paint 7 walls.
How many minutes does it take 9 people to paint 9 walls?
Found 3 solutions by ankor@dixie-net.com, josgarithmetic, josmiceli:
Answer by ankor@dixie-net.com(22740)   (Show Source):
You can put this solution on YOUR website!
It takes 49 minutes for 4 people to paint 7 walls.
Find how many man-minutes to paint one wall
= 28 man-minutes per wall
:
How many minutes does it take 9 people to paint 9 walls?
let m = no. minutes t do this
9m = 9*28
9m = 252
m = 252/9
m = 28 minutes for 9 men to paint 9 walls

Answer by josgarithmetic(39617)   (Show Source):
You can put this solution on YOUR website!
Let r be the one-person work rate.
n*r is the rate for n people working.
Use t as minutes.

Key idea is RT=J for rate, time, job
Uniform Rates for doing a job.

The amount of work is in unit of WALLS.

Examine that system so you understand how it makes sense.
Simplify, and solve for t.

Answer by josmiceli(19441)   (Show Source):
You can put this solution on YOUR website!
It takes 49 minutes for 4 people to paint 7 walls
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It takes 49/9 min for 36 people to paint 7 walls
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It takes ( 4/9)*49 min for 9 people to paint 7 walls
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It takes (1/7)*(4/9)*49 min for 9 people to paint 1 wall
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It takes (9/7)*(4/9)*49 min for 9 people to paint 9 walls
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It takes 28 minutes for 9 people to paint 9 walls
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Actually this is the same time for 1 person to paint 1 wall
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It takes 4*49 min for 1 person to paint 7 walls
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It takes (4/7)*49 min for 1 person to paint 1 wall

It takes 28 min for 1 person to paint 1 wall
Good thing to remember