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Question 283156: A car goes 30 miles per hour on a 1 mile track and on his second lap he wants his average speed to be 60 miles per hour. What is his speed on the second lap?(teacher said not 90 miles per hour)
Answer by Alan3354(69443)   (Show Source):
You can put this solution on YOUR website! A car goes 30 miles per hour on a 1 mile track and on his second lap he wants his average speed to be 60 miles per hour. What is his speed on the second lap?(teacher said not 90 miles per hour)
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It's not 90.
The 2nd lap at 90 mph will take 40 seconds. That's 2 miles in 2 2/3 minutes,
--> an overall average of 45 mph
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You might think that since he made the 1st lap 1/2 of 60 mph, he could do the 2nd at 2x 60 mph to average 60 mph overall.
The 2nd lap at 120 mph would take 30 seconds.
The total time for 2 miles would be 2.5 minutes, --> 48 mph for the 2 miles.
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1 mile at 30 mph takes 2 minutes.
2 miles at 60 mph also takes 2 minutes, so time is up - it's not possible to average 60 mph for the 2 laps from that point.
It's what is called a "trick question", the answer is surprising.
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However, the problem says, "on his second lap he wants his average speed to be 60 miles per hour" It doesn't say 60 mph overall.
To average 60 mph on the 2nd lap, he'd go 60 mph.
The wording is careless and ambiguous.
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