SOLUTION: Two cars leave a restaurant at the same time and travel in opposite directions. At the end of 3 hours, they are 300 miles apart. Find the rate of the slower car if one car travels

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Question 110306This question is from textbook
: Two cars leave a restaurant at the same time and travel in opposite directions. At the end of 3 hours, they are 300 miles apart. Find the rate of the slower car if one car travels at a rate 20 miles per hour faster than the other. I know the equation r=d/t, but how do you plug the info in when there are two parts. Thanks for your help! This question is from textbook

Answer by solver91311(24713) About Me  (Show Source):
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If they are 300 miles apart after 3 hours, then their speeds must add to 100 mph. r=300%2F3. So if one car is 20 mph faster than the other, let r = the slower car's rate, and r + 20 = the faster car's rate. Since the sum of the rates must be 100, we can write
:
r%2Br%2B20=100
2r%2B20=100
2r=80
r=40, which is the rate of the slower car.
:
Check:
If the slower car's rate is 40 mph, the faster car's rate must be 40 + 20 = 60 mph.
:
Using d=rt, the slower car must have traveled 40 * 3 = 120 miles, and the faster car must have traveled 60 * 3 = 180 miles. 120 + 180 = 300. Check!