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Question
If the first term of an A.P. is 5, the last term is 15 and the sum of first n terms is 30, then find the value of n.
Solution
a = 5
Tn = l = 15
Sn = 30
n = ?
Sn = `n/2(a + l)`
⇒ 30 = `n/2(5 + 15)`
⇒ 60 = n × 20
⇒ 3 = n
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