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Highway to Hell!

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Highway to Hell!

by zagcollins » Mon Jul 28, 2008 9:02 am
A certain car averages 25 miles per gallon of gasoline when driven in the city and 40 miles per gallon when driven on the highway. According to these rates, which of the following is the closest to the number of miles per gallon that the car averages when it is driven 10 miles in the city and then 50miles on the highway?

A.28
B.30
C.33
D.36
E.38
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by sudhir3127 » Mon Jul 28, 2008 9:16 am
I go with D 36.
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by ricky » Mon Jul 28, 2008 9:31 am
Gallons used in city = 10/25
Gallons used on Highway= 50/40

Total distance travelled= 10+50 = 60 miles

So average fuel used while covering these miles = Distance/Total fuel used
= (60)/(10/25 +50/40) = 36 approx.


Should Be D.
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by malolakrupa » Mon Jul 28, 2008 9:34 am
The answer is B

In the city 25 miles per gallon . Hence when it travles 10 miles , it uses 10/25 gallons.

Similarly on the highway it uses 5/4 gallons .

Now total gallons consumed is sum of the above which is 1.65 gallons . total distance travelled is 60 miles . Hence the average is 60/1.65 which is approximately 30 miles .

Let me know if I am incorrect.
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by malolakrupa » Mon Jul 28, 2008 9:35 am
Silly mistake guys . the answer is 36.
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by sudhir3127 » Mon Jul 28, 2008 9:36 am
malolakrupa
60/1.65 = 36.36.. i think u missed there...
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36

by hakyology » Mon Jul 28, 2008 9:42 am
Basically, this question asks if you know how to find "average speed".
Average speed = total distance / total time

city speed is 25
and total distance the city speed will go is 25 miles per gallon.<----this is the rate, amigo.

so don't forget the formula, distance= rate * time

10 = 25 t
t=2/5

then the rest 50 miles with 40 rate.
50= 40 t
t = 5/4

and then follow the formula.
total distance is 10 + 50 = 60 miles

average speed is 60 divided by total distance (2/5 + 5/4)


then you will get 36.3xxxxx

so the closest one is D, 36.



hope this helps.
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