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Question
Find the sum of 50 terms of the A.P. 1 + 4 + 7 + ..... .
Sum
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Solution
a = 1
d = 4 − 1
= 3
n = 50
Using `S_n = n/2 [2a + (n - 1)d]`
`S_50 = 50/2 [2(1) + (50 - 1)3]`
= 25[2 + 49 × 3]
= 25[2 + 147]
= 25 × 149
= 3725
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