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

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d = 7, a22 = 149, S22 = ? 

a = a + (n – 1)d 

a + (22 – 1)7 = 149 

a + 21 × 7 = 149 

a + 147 = 149 

=149 – 147

∴ a = 2

∴ Sn\(\frac{n}{2}\)[a + an]

S22 = \(\frac{22}{2}\)[2 + 149]

= 11[151] 

∴ S22 = 1661

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