Question 1172263
.
In driving to keep an appointment in another city. Harry estimated that he would arrive on time if he maintained a constant rate 
of 40 mph. When he was 10 mile from his destination, however, he was forced to detour over a longer route and reduce his speed 
to 30 mph. He arrived 15 minutes late. How long was the detour?
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            It can be solved mentally by reasoning,  without using equations



<pre>
When Harry was 10 miles from his destination, the expected time to arrive was  {{{10/40}}} = {{{1/4}}}  of an hour, or 15 minutes.


But moving detour, Harry spent 15 minutes + 15 minutes = 30 minutes = 0.5 of an hour.


Hence, the deture was  40 mph x 0.5 of an hour = 20 miles long.    <U>ANSWER</U>
</pre>

Solved.