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A car runs the first 5000 miles at 40 miles to the gallon of fuel and the next 5000 miles at 36 miles to the gallon. What is the average petrol consumption for the whole 10000 miles?

2006-11-25 08:28:25 · 5 answers · asked by John Frusciante 1 in Science & Mathematics Mathematics

5 answers

1st part:
5000 miles x (1 gallon/40 miles) = 125 gallons of fuel

2nd part:
5000 miles x (1 gallon/36 miles) = 138.89 gallons of fuel

Total:
10000 miles / (163.89 gallons) = 37.89 miles/gallon

You can't use the AVERAGE for expressions 1/a and 1/b as you would a and b

It's not 38 because:
10000 / (5000/36 + 5000/40) is not equal to: 10000 / (5000/38 + 5000/38)

5000/40 + 5000/36 = 125.00 + 138.89 = 263.89
5000/38 + 5000/38 = 131.58 + 131.58 = 263.16

2006-11-25 09:02:02 · answer #1 · answered by Anonymous · 0 0

Fuel used first 5000 miles =5000/40 =125 gallons
Fuel used 2nd 5000 miles = 5000/36= 138.888888 gallons Average (125 + 138.88888)/2 = 131.944444 gallons

2006-11-25 08:37:04 · answer #2 · answered by ironduke8159 7 · 0 0

Hm, I thought the answer would be 38 -- since the distances were equal -- but I'm not so sure anymore.

I tried to solve it by calculating the total amount of fuel used, and dividing it into the total number of miles.

5000 miles / 40mpg = 125 gallons on the first leg
5000 miles / 36mpg = 138.8889 gallons on the second leg

10000 miles / (125 + 138.8889 gallons) = 37.895 mpg

I feel like I should know why the two answers don't jive...perhaps someone else could explain that?

2006-11-25 08:39:35 · answer #3 · answered by Jim Burnell 6 · 0 0

Hi Since in this case the distances are equal you simply average the consumption, or 40+36 divided by 2.

2006-11-25 08:36:23 · answer #4 · answered by Cirric 7 · 0 0

38 miles?

2006-11-25 08:33:27 · answer #5 · answered by Zack C 3 · 0 0

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