A man runs 1 mile at a speed of r mph. If he runs at a speed of r+20 miles per hour, he would run the same distance in 4 minutes less. What is the value of r? Choose the correct choice:
A) 20 mph	B) 8 mph	C) 7 mph	D) 10 mph	E) 5 mph
Convert minutes to hours: 4 min = 4/60 min = 1/15 hours.   Equation: 1/r = 1/(r+20) + 1/15.   Plug options into the equation. D fits: 1/10 = 1/(10+20) + 1/15.   Answer: 10 mph
<result>D</result>
A man runs 1 mile at a speed of r mph. If he runs at a speed of r+20 miles per hour, he would run the same distance in 4 minutes less. What is the value of r?