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A driver traveled from A to B. On the return trip, he averaged 10kph more
and that trip took 30 minutes less.
If he had averaged 10 kph less on the outgoing trip, that trip would have taken 40 minutes more.
On the trip from A to B what was the average speed ?
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Let d be one way distance, r the average speed under the problem's question.
The time equation for the first scenario is
- = of an hour (1)
The time equation for the second scenario is
- = of an hour (2)
To find "r", divide equation (1) by equation (2). The common factor "d" will be canceled,
and after simplification you will get this equation for r
= ,
= ,
4*(r-10) = 3*(r+10),
4r - 40 = 3r + 30
4r - 3r = 40 + 30
r = 70.
ANSWER. The average speed under the problem's question was 70 kilometers per hour.
Solved.
By the way, knowing this average speed, it is easy to find one-way distance from A to B.
It is 280 kilometers.