Skier SARAH completes a straight 300-meter downhill run in t seconds and at an average speed of (x + 10) meters per second. She then rides a chairlift back up the mountain the same distance at an average speed of (x - 8) meters per second. If the ride up the mountain took 135 seconds longer than her run down the mountain, what was her average speed, in meters per second, during her downhill run? Choose the correct choice from the following answers:
A) 10 B) 15 C) 20 D) 25 E) 30
Backsolving is the preferred approach for this one   300/(x-8) - 300/(x+10) = 135   We are asked for the value of x+10   So we can start with 20 = X+10 = 20   So x = 10   300/2 - 300 / 20= 
<gadget id="calculator">300/2 - 300 / 20</gadget>
<output>135</output>
135   Hence answer is 20
<result>C</result>
Skier SARAH completes a straight 300-meter downhill run in t seconds and at an average speed of (x + 10) meters per second. She then rides a chairlift back up the mountain the same distance at an average speed of (x - 8) meters per second. If the ride up the mountain took 135 seconds longer than her run down the mountain, what was her average speed, in meters per second, during her downhill run?