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1) Car A and car B enter an expressway at the same time and place and head the same direction. Car A travels at 76 miles per hour.
After 3 hours, car B is 42 miles behind car A. What is the speed of var B?
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In 3 hours, car A traveled the distance of 3*76 = 228 miles.
At this time, car B was 42 miles behind car B. Hence, it traveled 228 - 42 = 186 miles in 3 hours.
Then the average speed of the car B is = 62 mph.
Solved.
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2) After dieting and excersing for several months, Sam now weighs 20% less than he did originally.
If Sam now weighs 180 pounds, how much did he weigh originally?
Let x be the Sam's original weight (which is under the question).
Then the problem says that (1-0.2)*x = 180 pounds, or 0.8x = 180,
which implies x = = 225 pounds.
It is your answer.