Question

1 ) During his morning commute to work in rush hour traffic, Justin's average speed was 30 mi/h. During his afternoon commute back home along the same route, his average speed was 60 mi/h. What was his average speed for the entire round trip?

15 points, answer correctly, please!

Answer 1

Answer:45 mi/h

Explanation:

Recall: Speed = distance / time

Let the time taken for the morning journey be
`t_(1)` and the time taken for the afternoon journey be
`t_(1)` ,and the distance covered be d

that means for the first journey,

30 =
`(d)/(t_(1))`

d = 30
`t_(1)`

Also for the afternoon journey,

d = 60
`t_(2)`

Equating the two , since the same distance is being covered , we have

30
`t_(1)` = 60
`t_(2)`

that is

`t_(1)` =
`(60t_(2))/(30)`

`t_(1)` = 2
`t_(2)`

Also ,

total distance covered = 30
`t_(1)` + 60
`t_(2)`

Average speed = total distance / total time

= 30
`t_(1)` + 60
`t_(2)` /
`t_(1)` +
`t_(2)`

Recall that
`t_(1)` = 2
`t_(2)` , substitute this into the formula for average speed , then we have

Average speed = 30(2
`t_(2)`) +60
`t_(2)` / 3
`t_(2)`

Average speed = 120
`t_(2)` / 3
`t_(2)`

Therefore :

Average speed = 40 mi/hr