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sukh: Senior | Next Rank: 100 Posts; Posts: 74; Joined: Tue Nov 09, 2010 11:33 pm

by sukh » Fri Aug 05, 2011 6:36 am

A 400-meter runner spent 4 more seconds on the first half of the distance than he did on the second. If the runner finished the 400-meter distance in 50 seconds, what was his average speed for the first 200 meters?(A) 24 1/3 (B) 25 1/3 (C) 26 2/3 (D) 27 2/3 (E) 29 1/2 all in kmph

If there are 10 liters of a 20%-solution of alcohol, how much water should be added to reduce the concentration of alcohol in the solution by 75% ? (A) 25 liters (B) 27 liters (C) 30 liters (D) 32 liters (E) 35 liters

Last edited by sukh on Sat Aug 06, 2011 6:57 am, edited 2 times in total.

Source: Beat The GMAT — Quantitative Reasoning | Fri Aug 05, 2011 6:36 am

pinchharmonic: Senior | Next Rank: 100 Posts; Posts: 51; Joined: Wed Aug 03, 2011 4:51 pm; Thanked: 2 times

by pinchharmonic » Fri Aug 05, 2011 1:07 pm

what units are the answers in? i'd assume same as the question, meters/sec. who runs 24m/sec?

Tani: Legendary Member; Posts: 1255; Joined: Fri Nov 07, 2008 2:08 pmFollowed by: 90 members; Location: St. Louis; Thanked: 312 times

by Tani » Sat Aug 06, 2011 11:40 am

THe answer in the first question don't make sense. 400 meters in 50 seconds is 8 meters per second. THe answer is going to be close to 8, not 25.

Total time 50 seconds, the first section is four seconds longer than the second section so we have
x + (x+4)= 50. That means our runner spent 27 seconds on the first 200 meters and 23 seconds on the second 200 meters. The rate on the first 200 is 200/27 meters per second. (approx. 7.4 mps)

For the second problem we have 10 liters total and 20% alcohol = 2 liters.

We are not changing the amount of alcohol so we will still have 2 liters in the new mixture.

Reducing the concentration by 75% means reducing 20% by 75%, leaving us with a target of 5% alcohol.

FOr 2 liters to be 5% of the total, the total must be 40 liters.

We started out with 10 liters and ended up with 40 so we added 30. Answer C

Tani Wolff

sukh: Senior | Next Rank: 100 Posts; Posts: 74; Joined: Tue Nov 09, 2010 11:33 pm

by sukh » Sat Aug 06, 2011 5:40 pm

Its Km per hour i guess we have to convert units

Tani: Legendary Member; Posts: 1255; Joined: Fri Nov 07, 2008 2:08 pmFollowed by: 90 members; Location: St. Louis; Thanked: 312 times

by Tani » Sat Aug 06, 2011 5:45 pm

correct: 7.4 meters per second *60 = 444 meters per minute * 60 = 26,640 meters per hour = approximately 26 2/3 kmph

Tani Wolff

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