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chaitanya.mehrotra: Master | Next Rank: 500 Posts; Posts: 184; Joined: Thu Nov 25, 2010 9:57 pmFollowed by: 5 members; Thanked: 1 times; GMAT Score:700

by chaitanya.mehrotra » Thu Aug 04, 2011 5:23 am

Castor trades in his old car, which traveled 16 miles per gallon of gasoline,
and buys a new car that travels 20 miles per gallon. Castor's brother Pollux
sells his hybrid, which traveled 50 miles per gallon, because he has built a
revolutionary new car that travels 100 miles per gallon. If both brothers
drive their cars 1000 miles to a family reunion, and gas costs $3.00 per gal-
Ion, which brother will have saved more money by switching cars, and by
how much?

Source: Beat The GMAT — Problem Solving | Thu Aug 04, 2011 5:23 am

vijaybhaskar_e: Newbie | Next Rank: 10 Posts; Posts: 2; Joined: Sun Jul 24, 2011 5:37 pm

by vijaybhaskar_e » Thu Aug 04, 2011 6:27 am

1) Castor would have spent 3*(1000/16) = $187.5 before car switch
Castor actually spent 3*(1000/20) = $150 after he switched to new car

Castor saved $(187.5 - 150) = $37.5 by switching to new car

2) Pollux would have spent 3*(1000/50) = $60 before car switch
Pollux actually spent 3*(1000/100) = $30 after he switched to new car

Pollux saved $(60 - 30) = $30 by switching to new car

Hence, Castor saved $7.50 more than Pollux did.

gmatboost: Master | Next Rank: 500 Posts; Posts: 312; Joined: Tue Aug 02, 2011 3:16 pmFollowed by: 33 members; Location: New York City; Thanked: 130 times; GMAT Score:780

by gmatboost » Thu Aug 04, 2011 7:11 am

To save time you can ignore the $3 since it is the same for everyone and just calculate the number of gallons each saved.

1000/16 = 500/8 = 250/4 = 125/2 = 62.5
1000/20 = 50
62.5 - 50 = 12.5

1000/50 = 20
1000/100 = 10
20 - 10 = 10

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