Question

Bill drove at an average of `65mph` for some time and then he drove at `55mph` for half the period. If he covered `925km.`, for how much time did he drive at `65kmph`?

Answer 1

Bill drove at an average of `65mph` for `10` hours.

Explanation:

Bill drove `925` miles. Let us assume he drove at an average of `65mph` for `x` hours. He covered `65x` miles during this period.

His average speed was `55mph` for half the period (as it is at slower rate) i.e. `x/2` hours. During this period, he covered `(55x)/2` miles.

As total distance covered is `925` miles, we have

`65x+(55x)/2=925`

or `130x+55x=925xx2=1850` (multiplying each term by `2`)

i.e. `185x=1850`

or `x=1850/185=10`

Hence, Bill drove at an average of `65mph` for `10` hours.