gmat prep question-work

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gmat prep question-work

by jc114 » Wed Apr 18, 2007 11:38 pm
Machine A can produce x products in 1 hour, machine B can produce x products in 3 hours. If machine A and B work together to produce x products, what is the ratio if the products that the faster machine can produce, to the total products?

A. 1/4
B. 1/2
C. 3/4
D. 1
E. 5/4

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by Cybermusings » Thu Apr 19, 2007 1:26 am
A-----x products ---- 1 hr

B----- x products ----- 3 hrs or x/3 products in 1 hr

A+B ------- 1 hr ------- (x + x/3) products = 4x/3 products

A+B -------- 4x/3 products ----- 1 hr

Therefore A+B -------- x products -------- [1/(4x/3)]*x = 3/4 hr

In 3/4 hr A would make 3x/4 products
Hence ratio = (3x/4)/x = 3/4
Hence C