Homework Help: algebra

Posted by Marta on Tuesday, April 27, 2010 at 11:13pm.

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A contractor finds that it takes a crew A 6 hours to construct a wall of a certain size. Crew B takes 8 hours to construct a wall of the same size. How long will it take if they work together?

algebra - Reiny, Tuesday, April 27, 2010 at 11:21pm
rate of A crew = wall/6
rate of B crew = wall/8
combined rate = wall/6 + wall/8
= 7wall/24

time with combined rate = wall/(7wall/24)
= 24/7
= 3.428 hours
= 3hours, 25.7 minutes

(notice the effective calculation was 1 ÷ (1/6 + 1/8)

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