One pipe can fill a pool 1.25 times faster than a second pipe. When both pipes are opened, they fill the pool in five hours. How long would it take to fill the pool if only the faster pipe is used?	Options
A) 11.25	B) 11.52	C) 1.25	D) 7.2	E) 9
Say the rate of the slower pipe is R pool/hour, then the rate of the faster pipe would be 1.25R=5R/4. Since when both pipes are opened, they fill the pool in five hours, then their combined rate is 1/5 pool/hour.   Thus we have that R + 5R/4 = 1/5 --&gt; R = 4/45 pool/hour, faster pipe fills at 1.25R which is 5/4 * 4/45 = 1/9 --&gt; time is reciprocal of rate thus it's 9/1= 
<gadget id="calculator">9/1</gadget>
<output>9</output>
9 hours.   Answer: 9.
<result>E</result>
One pipe can fill a pool 1.25 times faster than a second pipe. When both pipes are opened, they fill the pool in five hours. How long would it take to fill the pool if only the faster pipe is used?