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Re: Approach to solve Rate,Time work problems [#permalink]

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10 Sep 2012, 21:47

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If two typists can type two pages in two minutes, how many typists will it take to type 18 pages in six minutes? 3 4 6 12 36

Suppose rate of each typist is R So rate of two typist will be 2R time = 2mins work = 2pages using : Rate * Time = Work ,we have: 2R * 2 = 2 => R = 0.5 pages/min

Suppose x number of typist are required to finish 18pages in 6mins So, rate of R typist will be xR Time = 6mins work = 18pages Using Rate*time= work we have

xR * 6 = 18 => xR = 3 we know that R =0.5 => x = 6 So, answer will be C

If two typists can type two pages in two minutes, how many typists will it take to type 18 pages in six minutes?

A. 3 B. 4 C. 6 D. 12 E. 36

Could anyone plz explain a robust approach to solve above mentioned problem.I mostly get confused in RT=W probs.Thanks!

Since two typists can type two pages in two minutes, then one typists can type two pages in four minutes, which means that the rate of one typist is \(rate=\frac{job}{time}=\frac{2}{4}=\frac{1}{2}\) pages per minute.

Now, (combined rate of x typists)*(time)=(job) --> \((\frac{1}{2}*x)*6=18\) --> \(x=6\).

Re: If two typists can type two pages in two minutes, how many t [#permalink]

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11 Sep 2012, 05:38

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This post was BOOKMARKED

arkle wrote:

If two typists can type two pages in two minutes, how many typists will it take to type 18 pages in six minutes?

A. 3 B. 4 C. 6 D. 12 E. 36

Could anyone plz explain a robust approach to solve above mentioned problem.I mostly get confused in RT=W probs.Thanks!

2 typists 2 pages 2 minutes 2 typists 2*9=18 pages 2*9=18 minutes (9 times more pages, 9 times more time) 2*3=6 typists 18 pages 18/3=6 minutes (need 3 times faster, should increase number of typists by the same factor 3)

Answer C

This question is about direct and inverse proportionality. RxT=W (rate x time = work)

If work is constant, then R and T are inversely proportional, meaning if R increases, T decreases and vice-versa. If R is constant, then T and W are directly proportional, meaning if T increase, W increases (more time, more job done). If T is constant, then R and W are again directly proportional, meaning if R increases, W increases (faster rate, more job done).

In the above approach, first if we increase the number of pages (more work must be done), but we stay with the same number of typists, we need proportionally more time. Here, time and work are directly proportional. Then, for the same number of pages (same work), if we want the job done faster, we need more typists. Now, number of typists and time are inversely proportional.

This type of question reminds me of a home-work that would upset many parents (lamenting that this is insane ):

If one and a half chicken lay in a day and half one egg and a half, how many eggs will lay three chicken in three days?

Who heard of half chickens laying half eggs...those math teachers gone mad!!!
_________________

PhD in Applied Mathematics Love GMAT Quant questions and running.

Re: If two typists can type two pages in two minutes, how many t [#permalink]

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15 Nov 2012, 01:31

Let the individual rate of each typist be=\(\frac{1}{t}\)

Using the Rate equation Rt=W we can calculate their rates: \((\frac{1}{m}+\frac{1}{m})(2 minutes)=2pages==>\frac{2}{m}=\frac{2pages}{2minutes}==>m=2minutes\)

Thus, the individual rate of each typist =\(\frac{1page}{2minutes}\)

Now let's calculate the number of typists needed to work for 6 minutes to make 18 pages.

Re: If two typists can type two pages in two minutes, how many t [#permalink]

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21 Feb 2013, 21:47

To handle this type of problem efficiently I like to extend the R(T)=W formula ==> to #RT=W where # is number of people and RTW is still Rate, Time, Work. So for this problem:

Solve for R first #=2 typists R=? T=2 minutes W=2 pages

#RT=W==>2(R)(2)=2==>4(R)=2 divide both sides by 4 to get R=2/4 which is of course R=1/2. Now you have the rate PER TYPIST.

Now solve the rest of the question the same way to get # #=? R=1/2 T=6 minutes W=18 pages

#RT=W==>#(1/2)(6)=18==>#(3)=18 divide both sides by 3 and you get #=6. So 6 is the number of typists it will take to accomplish 18 pages in 6 minutes. Hope it helps.

Re: If two typists can type two pages in two minutes, how many t [#permalink]

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22 Feb 2013, 03:02

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More the no. of pages, more the no. of typist required. more the minutes available, lesser the no. of typist required. therefore, no. of typist is directly proportional to the no. of pages and inversely proportional to the no. of minutes Hence, No of typist = 2x(18/2)x(2/6) = 6

Re: If two typists can type two pages in two minutes, how many t [#permalink]

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22 Feb 2013, 03:15

If two typists can type two pages in two minutes, how many typists will it take to type 18 pages in six minutes?

A. 3 B. 4 C. 6 D. 12 E. 36

In 2 minutes 2 typists type 2 pages which means that in 6 minutes they will type 6 pages but to type 18 pages (3 times) we need 3 times more typists i.e. 2 x 3 = 6 typists.