Problema Solution

Tommy drove 40 mph to his grandmother's house one day. When he came home he took the same route but drove 45 mph. He drove a total of four hours. How many miles did he drive that day?

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solution:

 

d = rt

t = d/r

4 = d/40 + d/45

1440 = 9d + 8d = 17d

d = 1440/17 miles

d =~ 84.7 miles