SOLUTION: A car travels 120 miles. A second car traveling 10 mph faster than the first car.makes the same trip in 1 hr less time. Find speed of each car.

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Question 967395: A car travels 120 miles. A second car traveling 10 mph faster than the first car.makes the same trip in 1 hr less time. Find speed of each car.
Found 2 solutions by josgarithmetic, MathTherapy:
Answer by josgarithmetic(39621) About Me  (Show Source):
You can put this solution on YOUR website!
A car travels r miles. A second car traveling k mph faster than the first car.makes the same trip in h hr less time. Find speed of each car.


____________________rate___________time__________distance
SLOW________________r_______________t____________d
FAST________________r+k____________t-h___________d

r, unknown
k, 10
t, unknown
h, 1
d, 120

Uniform rates travel rule is RT=D...

system%28rt=d%2C%28r%2Bk%29%28t-h%29=d%29

Solve the system for the two unknown variables, t and r.

Answer by MathTherapy(10555) About Me  (Show Source):
You can put this solution on YOUR website!

A car travels 120 miles. A second car traveling 10 mph faster than the first car.makes the same trip in 1 hr less time. Find speed of each car.
Let speed of slower car be S
Then speed of faster car is: S + 10
We then get: 120%2FS+=+120%2F%28S+%2B+10%29+%2B+1
120%28S+%2B+10%29+=+120S+%2B+S%28S+%2B+10%29 ------- Multiplying by LCD, S(S + 10)
120S+%2B+1200+=+120S+%2B+S%5E2+%2B+10S
S%5E2+%2B+120S+%2B+10S+-+120S+-+1200+=+0
S%5E2+%2B+10S+-+1200+=+0
(S - 30)(S + 40) = 0
S, or speed of slower car = highlight_green%2830%29 mph OR S = - 40 (ignore)
Speed of faster car: 30 + 10, or highlight_green%2840%29 mph