Question 1002490: kale Average of 4 tests is 80. Which number of tests cannot be on which he earned exactly 80.
Answer by Theo(13342)   (Show Source):
You can put this solution on YOUR website! i would say it can't be 3.
it could be 0 because none of the test scores could be 80 and still have an average of 80.
if could be 1 because the other 3 could have an average of 80 which would make the total have an average of 80.
it could be 2 because the other 2 could have an average of 80 which would make the total have an average of 80.
it could be 4 because 4 * 80 / 4 = 80
if 3 are equal to 80, then the fourth have to be 80 in order for the average to be 80.
therefore it can't be 3.
examples:
none are 80: 60 100 70 90 total = 320 average = 80
1 is 80: 80 50 90 100 total = 320 average = 80
2 is 80: 80 80 90 70 total = 320 average = 80
3 is 80: 80 80 80 80 total = 320 average = 80 *****
if 3 are 80, the fourth have to be 80 as well, otherwise you can't get an average of 80.
therefore 3 can't be 80.
it's either 0, 1, 2, or 4 only.
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