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a ps from gmatclub

by diebeatsthegmat » Mon Aug 29, 2011 7:17 pm
Two swimmers start at opposite ends of a pool 89 feet long. One person swims at the rate of 19 feet per minute and the other swims at a rate of 53 feet per minute. How many times will they meet in 33 minutes?

A.13
B.11
C.10
D.8
E.5
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by smackmartine » Mon Aug 29, 2011 9:05 pm
IMO A
This was time consuming(3min+), but here is what I thought.

-->19ft/min <---53ft/min
|-------------|------------------------------|
________p1(Meeting Point for 1st time)


1st time cumulative distance covered is 89ft, which the length of the pool.
2nd time they meet total distance they have covered in 3 times the length of the pool.
...............5
...............7
Basically for nth time total distance covered is (2n-1)*89
As RT=D

R=(53+19)ft/min Relative speed.
T =33 min
So , 72*33 = (2n-1)*89

(2n-1)=(72*33)/89 ~ (72*33)/90 ~ 25.(something)

n~24.(something)/2 = 12.(something)

As n should be an integer and we have increased the denominator , possible value of n should be 13.
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by smackmartine » Tue Aug 30, 2011 12:50 am
OA pls. What's the source?
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by diebeatsthegmat » Wed Aug 31, 2011 6:04 pm
smackmartine wrote:OA pls. What's the source?
OA is 13 and i also did it 13 but to be honest, it took me 2 mins and 15 seconds to do it so i wanted to know if there is any other solusion to do it faster... its from Gmatclub. who knows the source but i did the gmat test once and i realize that word problem's question in the gmat test is so many and complicating... it askes us to really understand the form to do the math... so i do every question about word problem's problem...
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