Find the sum of first 22 terms of an AP in which *d* = 7 and 22^{nd} term is 149.

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#### Solution

*d* = 7

*a*_{22} = 149

*S*_{22} = ?

*a*_{n} = *a* + (*n* − 1)*d*

*a*_{22} = *a* + (22 − 1)*d*

149 = *a* + 21 × 7

149 = *a* + 147

*a* = 2

`S_n = n/2(a+a_n)`

`=22/2(2+149)`

= 11(151)= 1661

Concept: Sum of First n Terms of an AP

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