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# From A to B, 20 miles per gallon of gas; from B to A,

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Manager
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From A to B, 20 miles per gallon of gas; from B to A, [#permalink]

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04 Mar 2008, 10:25
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From A to B, 20 miles per gallon of gas; from B to A, different route, 25 miles per gallon of gas. What is the average gas per mile for the round trip?
(1) round trip is 175 miles long.
(2) from B to A the distance is 3/4 of distance from A to B.

Please kindly provide explanations for the following question
Director
Joined: 09 Aug 2006
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04 Mar 2008, 11:15
az780 wrote:
From A to B, 20 miles per gallon of gas; from B to A, different route, 25 miles per gallon of gas. What is the average gas per mile for the round trip?
(1) round trip is 175 miles long.
(2) from B to A the distance is 3/4 of distance from A to B.

Please kindly provide explanations for the following question

Is it C .. ?? I guess it is ..

St1 : Only the total distance. We need total distance and the total fuel consumed.. ---- Insuff.

St2 : AB = x, BA = 3/4x .. That's it what we get from this statement. --- Insuff.

St1 &2 , x+3/4x = 175

AB = 100, BA = 75 and the rest all taken care of .. Suff..

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Manager
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04 Mar 2008, 11:37
Its C

To find average gas/mile we need total miles and total gas consumed
we already have averages for individual trips
AB : 20 miles/gallon
BA : 25 miles/gallon

Statement 1 : Gives total mile but no info on total gas insuff.
statement 2 : Gives relation between miles not much info to find required average
Both together :
Let AB=x
BA=y
so y=3/4x
x+y=175
we have independent averages so we can find total
from this info.
SVP
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04 Mar 2008, 12:08
im getting C.

From stat1, i just know the gallon/mile number for both legs, and the total distance. however, i dont know how much A to B and B to A is. Insuff.

From stat2, i just know that B to A is 3/4 of A to B, i.e. y=3/4x. This would still leave the equation with one variable. Insuff.

Together, we have everything we need. We can figure out the distance of one leg, and subsequently the other using x+y=175, and we're done.
CEO
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04 Mar 2008, 14:54
az780 wrote:
From A to B, 20 miles per gallon of gas; from B to A, different route, 25 miles per gallon of gas. What is the average gas per mile for the round trip?
(1) round trip is 175 miles long.
(2) from B to A the distance is 3/4 of distance from A to B.

Please kindly provide explanations for the following question

Must be C. this was my initial answer in the begining. However, being a GMAT problem I double checked S2.

Just use the miles from S1: 175. we get AB=100 and BA=75.

Use another one 140 miles. we get AB=80 and BA=60.

100/20=5 75/25=3 8m/gal

80/20=4 60/25 = 12/5 ---> 32m/5gal.

Not the same

Thus I stand by C.
Director
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04 Mar 2008, 17:24
I would go for 'B'.

Stmt1: Clearly insuff

Stmt2: let's say the AB = s
BA = 3/4 s
Average gas per mile for the round trip = total miles/total gas consumed
total miles = s + 3/4 s
total gas = s/20 + 3/4 s/25
we can calculate the average gas per mile from the give info as 's' will cancel out from numerator and denominator.
hence suff
Manager
Joined: 12 Feb 2008
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04 Mar 2008, 18:33
vshaunak@gmail.com wrote:
I would go for 'B'.

Stmt1: Clearly insuff

Stmt2: let's say the AB = s
BA = 3/4 s
Average gas per mile for the round trip = total miles/total gas consumed
total miles = s + 3/4 s
total gas = s/20 + 3/4 s/25
we can calculate the average gas per mile from the give info as 's' will cancel out from numerator and denominator.
hence suff

I did C but vshaunak’s answer sounds intriguing.
What is the OA?
VP
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04 Mar 2008, 21:17
az780 wrote:
From A to B, 20 miles per gallon of gas; from B to A, different route, 25 miles per gallon of gas. What is the average gas per mile for the round trip?
(1) round trip is 175 miles long.
(2) from B to A the distance is 3/4 of distance from A to B.

Please kindly provide explanations for the following question

average gas per mile for the round trip = Tot distance/Tot nos of gallons of gas used

1.gives distance but does not get info about amount of gas consumed ->INSUFF
2. let d be dist between A nd B
20 = d/g1 , 25 = .75 d/g2

g1 = d/20, g2 = .75d/25

Tot distance = 1.75d

Tot nos of gallons of gas used = g1+g2 =d/20+ .75d/25

B is suff
Manager
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04 Mar 2008, 21:32
Thanks everyone for discussion!
OA is B.

From A to B, 20 miles per gallon of gas; from B to A, different route, 25 miles per gallon of gas. What is the average gas per mile for the round trip?
(1) round trip is 175 miles long.
(2) from B to A the distance is 3/4 of distance from A to B.

Average gas per mile = (volume of gas from A to B + volume of gas from B to A)/(distance from A to B + distance from B to A).
(1) is insuff.
(2) let the distantce from A to B as d1, then d1/20 gallon of gas; let the distantce from B to A as d2, d2= 3d1/4/25=3d1/100 gallon of gas. The average is (d1/20+3d1/100)/(d1+3d1/4)=8/175. SUFF
Re: DS (rates)   [#permalink] 04 Mar 2008, 21:32
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