Easy SAT Math Question

Please show all steps! In three separate 1-mile races, Ellen finishes with times of x minutes, y minutes, and z minutes. What was her average speed, in miles per hour, for all three races? (1 Hour=60 minutes).

I know the answer is 180/x+y+z
But I don't know how you get to that step.

I got 3/(x+y+z)/60
then I did this 3/(x+y+z) *1/60
= 1/20(x+y+z)
Can anyone tell me the mistake I made?

Since you got 3 / ((x+y+z) / 60)

When you have a number over a number divided by another number, you simply take the reciprocal and multiply.

So from 3 / ((x+y+z) / 60)
you get ::: 3 * (60 / x+y+z)

= 180 / x+Y+z

For example if you have 4 divided by 1/2...

4/ (1/2) its the same as 4 / 0.5

4 * (2/1) = 8
4 / 0.5 = 8

In three separate 1-mile races, Ellen finishes with times of x minutes, y minutes, and z minutes. What was her average speed, in miles per hour, for all three races? (1 Hour = 60 minutes).
(x + y + z)/60/3
= (x + y + z)/20

Average speed in miles per hour:
= 3/(x/60 + y/60 + z/60)
= 3/([x + y + z]/60)
= 3(60/[x + y + z])
= 180/(x + y + z)

Answer: 180/(x + y + z)