Question 1168709
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The times are the same, so the ratio of distances is equal to the ratio of speeds:<br>
{{{156/168 = x/(x+5)}}}<br>
You can certainly solve this using formal algebra.  But you can also solve it (I think a bit more quickly) solving it using equivalent fractions.<br>
{{{156/168 = (12*13)/(12*14) = 13/14}}}<br>
In that simplified fraction the difference between the numerator and denominator is 1.  The problem tells us we want an equivalent fraction in which that difference is 5.  So get an equivalent fraction by multiplying numerator and denominator by 5:<br>
{{{13/14 = (13*5)/(14*5) = 65/70}}}<br>
ANSWER: his average speed is 65mph (it would be 70mph if he had been driving 5mph faster).<br>