math
posted by kate .
Sue was in excellent shape in high school, she could ride her 10speed 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)(xy) = 4.8
14x  14y = 288
1st time 14 > 164x + 154y = 4032
2nd times 11 > 154x  154y = 3168
add them
318x = 7200
x = 22.64
sub into 11x + 11y = 288 to get
y = 3.54
check my arithmetic