Speed trouble problem

Algebra Level 2

It took Brian 6 hours to drive to the sales conference. He took the same route back, but this time it took 7 hours. (No difference in traffic) if he drove 9 mph faster on his way to the conference, how fast did he drive on the way back home ?

43 90 54 88 58

David Warrak by David Warrak , 18, USA

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1 solution

David Warrak
Jun 6, 2018

This is a harder problem than many others. It took me awhile to figure it out myself. To solve this, the best way is to translate it into an equation, and then solve it. and here is the formula: The distance to the conference has to equal the time back . And distance equals speed multiplied by time.

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We can set up 2 equations, for unknown distance D D and slower velocity v v

d v = 7 \dfrac{d}{v}=7
d v + 9 = 6 \dfrac{d}{v+9}=6

Solving them gets you d = 348 d=348 miles and v = 54 v=54 mph.

Michael Mendrin - 3 years ago

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Thanks that helps:)

David Warrak - 3 years ago

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