The sum of the first 10terms is 55
---> (10/2)(2a + 9d) = 55
2a + 9d = 11
the sum of the last 10 terms is 355
---> the sum of all 20 terms is 355+55 = 410
10(2a + 19d) = 410
2a + 19d = 41
subtract them:
10d = 30
d = 3
sub into 2a + 9d = 11
2a + 27 = 11
2a = -16
a = -8
a = -8 , d = 3
There are 20 terms in AP. The sum of the first 10terms is 55 and the sum of the last 10 terms is 355.find the first term and the common difference
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