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 Forum Index >  Test Paper Related >  Primary 5 Matters
 rate and proportion question
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By: keenlearner (offline)  Friday, November 09 2012 @ 05:40 AM CST (Read 709 times)  
keenlearner

Hi, can anyone teach me how to solve this question. Thanks!

It takes 3 cleaners 2/9 hr to clean an office. How long do 5 cleaners take to clean the same office, assuming every cleaner clean at the same rate?

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By: jo sarah (offline)  Saturday, November 10 2012 @ 07:49 AM CST  
jo sarah

It takes 3 cleaners 2/9 hr to clean an office. How long do 5 cleaners take to clean the same office, assuming every cleaner clean at the same rate?

1/3 of the office is cleaned by a cleaner in 2/9 hr
1 whole of the office will be cleaned by a cleaner in 2/9 x 3 = 2/3 hr
So, 1/5 of the office will be cleaned by a cleaner in 2/15 hr

therefore, the 5 cleaners will clean the same office in 2/15 hr
[because each of the 5 cleans 1/5 of it.]

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alternatively, if you understand that for the same piece of work (cleaning the same office),
more cleaners will take less time, then,

the time taken will be (3/5) x (2/9) hr = 2/15 hr

Smile

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