Answers

2015-05-19T11:33:22+05:30
Sum of 15 terms(S15) = 1290
Sum of 16 terms(S16) = 1464

16th term (t16_) = S16 - S15 = 1464 - 1290 = 174

S_{16} =  \frac{16}{2}(a + t_{16})

1464 = 8(a + 174)

a + 174 = 183
 a = 9

t16 = a + 15d

174 = 9 + 15d

15d = 165

d = 11

S_{n} = \frac{n}{2}(2a + (n-1)d)
S_{20} = \frac{20}{2}(2(9) + (20-1)11)
S_{20} = 10(18 + 209)
S_{20} = 10(227)
S_{20} = 2270
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