SOLUTION: David knew he made a mistake when he calculated that Gilda walks 123 miles to the station. Read through David's calculations: Using d = rt, the distance is the same, but the rat

Question 1079804: David knew he made a mistake when he calculated that Gilda walks 123 miles to the station. Read through David's calculations:
Using d = rt, the distance is the same, but the rate and time are different.
If Gilda misses the train, it means the time t needs 7 more minutes at a rate of 3 mph, so d = 3(t + 7).
If she gets to the station 5 minutes early it means the time t can be 5 minutes less at a rate of 4 mph so d = 4(t - 5).
3(t + 7) = 4(t - 5)
3t + 21 = 4t - 20
t = 41
d = rt, so d = 3(41) = 123
Find David's mistake in his calculations. In two or more complete sentences, explain his mistake. Include the correct calculations and solutions in your answer.
Answer by MathLover1(20849) (Show Source): You can put this solution on YOUR website!

Two mistakes.
Time is measured in minutes.
Rate is measured in miles/hour.
You must convert one of them to be consistent.

Answer is the same but the units are now correct.
When you measured distance, you have to use either of the formulas,

If you use , you'll get the wrong answer since and would give you different answers.

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