Question 1191407: Find the sum of AP whose first term is 60 and last term is -104
Answer by greenestamps(13203)   (Show Source):
You can put this solution on YOUR website!
Not enough information. We need some information from which we can determine the number of terms.
The sum of the terms of an AP is the number of terms, multiplied by the average of all the terms; and in an AP the average of all the terms is the average of the first and last terms.
The average of the first and last terms in this example is (60-104)/2 = -22.
So if the number of terms is n, the sum of the terms is -22n.
2 terms: 60, -104
sum: -44 = 2(-22)
3 terms: 60,-22,-104
sum: -66 = 3(-22)
4 terms: 60,16/3,-148/3,-104
sum: -88 = 4(-22)
etc....
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