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Old 07-24-2007   #4
Katie I
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1. To find an average, you have to add all the separate units and divide by the total number of units. In this case, 45 mph (the average) is equal to the sum of how fast she drove each hour divided by 6. So, 6*45 = 270, and therefore 270 = the sum of how fast she drove each hour. If she drove 53 mph for the first 2 hours, you can subtract 106 from 270 = 164. Therefore, to find the average of how fast she drove for the last 4 hours, divide 164/4 = 41. 41mph is the answer.2. distance = rate*time. Therefore, distance/rate = time. 118/60 = 1.9666 hours going there118/72 = 1.6388 hours coming backAdd the two to find the total hours. He drove a total of 3.6 hours.3. Use the same equation from above. Distance = rate*time. You distance, you know rate, so you can find out how much time it took and then subtract that from the arrival time.39/51 = .765 hour = 45.88 minutes2:58 - 45.88 = 2:12pm