Question:
The first and the last terms of an AP are 17 and 350 respectively. If the common difference is 9, how many terms are there and what is their sum?
Answer:
Let first term of AP = a
Last term of AP = l
common difference = d
l =a + (n-1)*d
=>350 = 17 + (n-1)*9 (Given l =350, a = 17 and d = 9)
=>350-17 = (n-1)*9
=>333 = (n-1)*9
=>n-1 = 333/9
=> n-1 = 37
=>n = 37+1
=> n =38
Now sum of AP = (n/2)*(a + l)
=> (38/2)*(17 + 350)
=> 19*367
=> 6973
So number of terms in AP is 38 and sum is 6937
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