Problem: A boat has a speed of 15 m.p.h. in still water. In a stream that has a current of 5 m.p.h. it travels a certain distance downstream and returns. The ratio of the average speed for the round trip to the speed in still water is:
Answer Choices:
A. 5/4
B. 1/1
C. 8/9
D. 7/8
E. 9/8
Solution:
x2=201+101,x=340,15x=1540/3=98