Find the sum of the first 22 terms of an ap in which d=7 and 22nd term is 149
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GIVEN :
Common Difference(d) of an AP = 7
22nd term if AP = 149
a + 21d = 149
=> a + 21(7) = 149
=> a + 147 = 149
=> a = 149 - 147
=> a = 2
First-term (a) = 2
We know that sum of terms in an AP, Sn = n/2 [ 2a + (n - 1)d ]
Sn = 22/2 [ 2(2) + (21)7 ]
= 11 [ 4 + 147 ]
= 11 [ 151 ]
= 1661
Therefore, sum of first 22 terms is 1661.
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