SOLUTION: Thelma's average driving speed is 15 miles per hour faster than Kirk's. in the same length of time it takes Thelma to drive 114 miles, Kirk only drives 84 miles. What is Thelma's a

Question 706061: Thelma's average driving speed is 15 miles per hour faster than Kirk's. in the same length of time it takes Thelma to drive 114 miles, Kirk only drives 84 miles. What is Thelma's average driving speed?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Thelma's average driving speed is 15 miles per hour faster than Kirk's. in the same length of time it takes Thelma to drive 114 miles, Kirk only drives 84 miles. What is Thelma's average driving speed?
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Kirk DATA:
rate = x mph ; distance = 84 miles ; time = d/r = 84/x hrs
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Thelma DATA:
rate = x+15 mph ; distance = 114 miles ; time = d/r = 114/(x+15)
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Equation:
time = time
84/x = 114/(x+15)
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Cross-multiply:
114x = 84x + 84*15
30x = 84*15
x = (1/2)84
x = 42 mph (Kirk's rate)
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x + 15 = 57 mph (Thema's rate)
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Cheers,
Stan H.
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