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Two boys can mow a lawn in 2 hours thirty minutes. If 3 other boys hel

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Two boys can mow a lawn in 2 hours thirty minutes. If 3 other boys hel [#permalink]

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New post 28 Mar 2017, 02:38
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Question Stats:

89% (00:42) correct 11% (00:45) wrong based on 56 sessions

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Two boys can mow a lawn in 2 hours thirty minutes. If 3 other boys helped, how long would it take to mow the same lawn with all of them starting at the same time, each working at their independent rate?

(1) All of the boys work at the same rate.
(2) The boys started mowing at 6 a.m.

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Re: Two boys can mow a lawn in 2 hours thirty minutes. If 3 other boys hel [#permalink]

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New post 29 Mar 2017, 02:02
stat 1 : given two boys can mow in 2hrs 30 mins,, and all have same rate,,, which means individual rates can be calculated..
suff
stat 2 : no info abt rate..

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Two boys can mow a lawn in 2 hours thirty minutes. If 3 other boys hel [#permalink]

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New post 21 May 2017, 05:13
Bunuel wrote:
Two boys can mow a lawn in 2 hours thirty minutes. If 3 other boys helped, how long would it take to mow the same lawn with all of them starting at the same time, each working at their independent rate?

(1) All of the boys work at the same rate.
(2) The boys started mowing at 6 a.m.


First Method : Correct

2 boys mow the lawn in 150 min .

Statement 1 : Both boys work at the same rate . Ra = Rb

Amt = 2 Ra * 150 == > Ra = Amt /300 ==>

Amt = 5 Amt /300 * t

t = 60 min = 1 hr .

Bunuel : I have 1 doubt

If the rate is same than Time is also same to do the same work .

Now in this question , why cant I say after reading the first statement , if they worked together than together they take 75 mins. (because their

combined rate is twice their individual rate).

and when 5 of them worked together than they will take 15 mins . (which i think is wrong).
Two boys can mow a lawn in 2 hours thirty minutes. If 3 other boys hel   [#permalink] 21 May 2017, 05:13
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