Toni is selling caps for the baseball club. The picture shows the number of caps that Toni sold during the first three weeks.
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Week 1
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* * * * * * * * *
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Week 2
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* * * * * *
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Week 3
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* * *
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Week 4
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?
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How many hats must Toni sell in week 4 so that the average number of caps that she has sold per week is 7?
Solution
There are a number of ways of tackling this problem. We’ll do it using the definition of average. So, the average is the number of caps sold altogether divided by the number of weeks. This is something divided by 4. But we know that the average is to be 7. Since something divided by 4 = 7, then the something must be 28. So Toni has to sell 28 caps over the 4 weeks.
Now add up all the caps she has sold. There were 9 in the first week, 6 in the second and 3 in the third. This is a total of 18. But she has to sell 28 to keep the average of 7. So Toni has to sell another 10 caps in the last week. The answer is therefore 10 caps.