miles per gallon

[tacobell]

A car averages 25 miles per gallon in the city and 40 miles per gallon on highway. According to these rates, which of the following is closest to the number of miles per gallon that the car averages when it is driven 10 miles in the city and 50 miles on the highway.
28
30
33
36
38
Thanks in advance.

[ajguerre]

Answer is 36.

Remember that the formula for average speed = Total Dist / Total Time

You need to find the time is takes to go 10 miles in the city as well as the time it takes to go 50 miles in the highway at their respective rates.

So for City: t1 = d1 / v1 = 10 / 25 = 2 / 5

For Highway: t2 = d2 / v2 = 50 / 40 = 5 / 4

Now sum the times t1 + t2 = 2/5 + 5/4 = 33/20

And then calculate the average speed by using the formula that I specified at the beginning of the post:

A = Total Dist / Total Time = (10 + 50) / (33/20) = 400 / 11 = 36.3

Since the question asks you to approximate then 36 is the answer.