Problem: A man walked a certain distance at a constant rate. If he had gone 21 mile per hour faster, he would have walked the distance in four-fifths of the time; if he had gone 21 mile per hour slower, he would have been 221 hours longer on the road. The distance in miles he walked was
Answer Choices:
A. 1321
B. 15
C. 1721
D. 20
E. 25
Solution:
Let D, R, T denote the distance (miles), rate (miles per bour), time (howrs) respectively. Then
D=RT,D=21(R+21)T,D=(R−21)(T+221)
The first and second equations give 21D=53T.∴D=2T.∴2T=RT and R=2. Repiacing T by 21D and R by 2 in the third equation gives D=53(21D+221),D=15 miles.