Answer: 60 mph
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Explanation:
R*T = D is the same as D = R*T
The D value is unknown, but it is the same for both cars since each car traveled the same distance.
The rate or R value for car A is some unknown x. For car B, R = x+15 because it traveled 15 mph faster than car A.
For car A, T = 2. For car B, T = 1.5
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The equation for car A is going to be D = x*2 or D = 2x. Note how I replaced R and T with x and 2 respectively.
The equation for car B is D = (x+15)*1.5 which distributes and simplifies to D = 1.5x+22.5
Because we're dealing with the same D value for both equations, we can equate the two right hand sides and solve for x
D = 2x
1.5x+22.5 = 2x ..... replace D with 1.5x+22.5
22.5 = 2x-1.5x
22.5 = 0.5x
0.5x = 22.5
x = 22.5/0.5
x = 45
So car A's speed was 45 mph. Add on 15 to get
x+15 = 45+15 = 60
which is car B's speed
side note: car A travels a distance of D = R*T = 45*2 = 90 miles; while car B travels a distance of D = R*T = 60*1.5 = 90 miles. Both cars traveling the same distance helps us confirm we have the right answer.
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So this is why the final answer is 60 mph
