<PRE><B>Question 929035</B>
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for tutor @CubeyThePenguin....&lt;br&gt;
(1) Your cryptic calculations with no explanation are of no use to the student who is trying to learn how to solve the problem.&lt;br&gt;
(2) I can&#39;t tell what the calculations you show are supposed to be doing to solve the problem.  Remember, your purpose as a tutor here is not to show that you know how to solve a problem; your purpose is to help the student learn how to solve the problem.&lt;br&gt;
(3) And in this case, whatever your calculations were supposed to be doing, they gave the wrong answer....&lt;br&gt;
************************************************************************************************&lt;br&gt;
Informally, the solution is simple.  Since the stopping distance varies directly as the square of the speed, a speed 5 times as great means a stopping distance 5^2=25 times as great.  ANSWER: 25(20 feet) = 500 feet.&lt;br&gt;
More formally....&lt;br&gt;
{{{d = kr^2}}}&lt;br&gt;
Find the constant of proportionality knowing that the stopping distance is 20 feet at 20mph.&lt;br&gt;
{{{20 = k(20^2)}}}
{{{20 = 400k}}}
{{{k = 1/20}}}&lt;br&gt;
Use that constant to find the sopping distance if the speed is 100mph.&lt;br&gt;
{{{d = kr^2}}}
{{{d = (1/20)(100^2) = 10000/20 = 500}}}&lt;br&gt;
ANSWER: 500 feet&lt;br&gt;
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