MATH question [easy] for Geniuses of course?

Question

a motorist travels 90 miled at a rate of 20 miles per hour. if he returns the same distance at a rate of 40 miles per hour, what is his average speed for the entire trip, in miles per hour?

please show work

Answer 1

90 miles at 20 mph takes 90/20 = 4.5 hours

90 miles at 40 mph takes 90/40 = 2.25 hours

That's 180 total miles in 6.75 hours and average speed is total distance divided by total hours, so 180 / 6.75 = 26.6 repeating (26 2/3 ) mph

Answer 2

the first guy is right, take both speeds (40, 20), and find the average. to do this, add the two and divide by the number of variables (2)....

40+20=60     60/2=30

Answer 3

Well I just asked someone ... Martin.  Martin doesn't know ... Martin did my taxes.

Answer 4

first, find time to:

s = d / t

t = 4.5 hours

now, find time of return trip:

s = d / t

t = 2.25 hours

lastly, take total distance divided by total time to find average speed:  

180 / 6.75 = about 27 mph

Answer 5

To find the total trip time add 90/40 and 90/20.  This give us 4.5 + 2.25.  Thus the total trip took 6.75 hours.  Since they travelled 180 miles you can find the average rate of speed by dividing 180 by 6.75 which gives an average rate of speed of 26.67 mph.

Answer 6

4.5 hours there, 2.25 hours return. so he goes at an average of 27.33 miles per hour.

Answer 7

It doesn't matter how far he traveled, only the speeds. Simply find the mean of 20 and 40, which is 30.