



 
Hi, If you drive 40 feet in one tenth of a second then in ten times that long (1 second) you travel ten ties as far(400 feet). Thus you are driving at the rate of 400 feet per second. This is a perfectly good answer but I expect you want it expressed in miles per hour. Let's do it in steps, first converting seconds to minutes. There are 60 seconds in a minute so in 60 times 1 second you travel 60 times 400 feet. Hence you are travelling at $60 \times 40$ feet per minute. How many minutes are in an hour? What is your speed in feet per hour? How many feet are in a mile? What is your speed in miles per hour? Penny  


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