Question 1019106
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Ling lives 2 miles from school. It took him 15 minutes to bike from school to home. The first half of the distance 
he biked at a speed of 12 mph. What was his speed for the remaining distance? What was his average speed?
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"the first half of the distance he biked at a speed of 12 mph".
So, Ling biked 1 miles at the speed of 12 mph = {{{12/60}}} = 0.2 miles per minute. 
Thus Ling spent {{{1/0.2}}} = 5 minute to cover the first half of the distance.

For the second half, which is also 1 mile, Ling spent the remaining 15-5 = 10 minutes, i.e. twice the time he spent for the first mile. 
It means that his speed was half of the speed on the first mile, {{{12/2}}} = 6 mph.

It is the answer to the first question.

Regarding the average speed, it is the FULL distance divided by the FULL time, i.e. {{{v[aver]}}} = {{{2/((1/4))}}} = 2*4 = 8 mph. 
(Here {{{1/4}}} is 15 minutes = 1/4 of an hour.)

<U>Answer</U>. The Ling's speed on the second half of the distance was 6 mph.
               The average speed was 8 mph.


The solution by jorel555 is wrong in this part.
The error he made is TYPICAL and represents the good/classic example on how this problem SHOULD NOT be solved. 
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