posted by kate .
Sue was in excellent shape in high school, she could ride her 10-speed bicycle 4.8miles to her grandmother's house in 11 minutes. Her return trip home took 14 minutes. The times are different due to there being a slight downhill slop on part of the trip to her grandmothers. If sue was able to ride her bike on a perfectly flat surgace with no hills, how fast can she travle in miles/hour?
her speed on flat ground --- x mph
effect of hill -------------- y mph
(11/60)((x+y) = 4.8
11x + 11y = 288
(14/60)(x-y) = 4.8
14x - 14y = 288
1st time 14 ---> 164x + 154y = 4032
2nd times 11 --> 154x - 154y = 3168
318x = 7200
x = 22.64
sub into 11x + 11y = 288 to get
y = 3.54
check my arithmetic