in an AP the sum of first n terms is - 150 and the sum of its next 10 terms is -550. find the AP
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The sum of the first and the 20th term of the AP
a+a+19d = 88, or
2a+19d = 88 …(1)
The 10th term is
a+9d = 42, or
2a+18d = 84 …(2)
Subtract (2) from (1)
d = 4.
Hence a = [88-(19*4)]/2 = [88–76]/2 = 8/2 = 4.
The 11th term = a +10d = 4 + 10*4 = 4+40 = 44.
The common difference = 4.
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