prep rate question

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jamesk486: Master | Next Rank: 500 Posts; Posts: 141; Joined: Wed Mar 28, 2007 9:24 pm; Thanked: 2 times; Followed by:1 members

prep rate question

by jamesk486 » Mon Aug 24, 2009 9:44 pm

If Mary always takes the same route to work how long did it take mary to get to work on Friday?

(1) It took Mary 20 minutes to get to work on Thursday
(2) Mary's average speed on her trip to work was 25% greater on Thursday than it was on Friday.

By looking at the two statements, I know what the answer is, but i'd like to understand how the answer comes out to!

Thanks!

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Source: Beat The GMAT — Data Sufficiency | Mon Aug 24, 2009 9:44 pm

hpgmat: Senior | Next Rank: 100 Posts; Posts: 75; Joined: Thu Aug 20, 2009 11:55 am; Location: vancouver, B.C; GMAT Score:640

Re: prep rate question

by hpgmat » Mon Aug 24, 2009 9:58 pm

jamesk486 wrote:If Mary always takes the same route to work how long did it take mary to get to work on Friday?

(1) It took Mary 20 minutes to get to work on Thursday
(2) Mary's average speed on her trip to work was 25% greater on Thursday than it was on Friday.

By looking at the two statements, I know what the answer is, but i'd like to understand how the answer comes out to!

Thanks!

we know D = T x V

Distance is a constant , So D (thursday) = D (friday)
...> T (thur) x V (thur) = T (fri) x V (fri) , we know that V (thur) = 1.25 x V (fri) and T (thur) = 20 min. So,

1.25 x T (thur) = T (fri)

T (fri) = 1.25 x 20

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