Math question involving D=RT

Question

A runner competes in a 6-mile race. The year before her speed was 3mph slower and it took her one hour longer. What was her speed this year?

 

How do I solve this? Thank you.

Answer 1

Start with D = RT

 

This year 6 = RT

6 / R = T                   You could also solve for R.

 

Last Year 6 = (R - 3)(T + 1)           Substitute for T

6 = (R - 3)((6/R + 1)

6 = 6 - 18/R + R - 3

0 = R - 18/R - 3

0 = R² - 3R - 18

0 = (R - 6)(R + 3)

 

R = 6   (can't go a negative mph)

T = 1