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It took Eric 11 hours to drive to a football game. On the way home, he was able to increase his average speed by 12 mph
and make the return drive in only 9 hours. Find his average speed on the return drive.
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Let x be Eric's average speed on the way to a football game, in mph.
Then his average speed on the return trip was (x+12) mph.
You have this equation
11x = 9*(x+12). (*)
Left side is the distance from Eric's home to the football game.
Right side is the same distance.
From (*),
11x = 9x + 108, or
2x = 108. Hence, x = = 54 mph.
Then Eric's average speed on the return drive was 12+x = 54 + 12 = 66 mph.
Answer. 66 mph
By the way, there is a simple criterion whether you do understand how to solve Travel and Distance problems.
If you are able to write the governing equation for the problem at once, you do understand.
If you are not able to write the governing equation for the problem at once, you do not understand.
The goal of training in Travel and Distance problems is to learn how to write the governing equation/equations at once.