Q. 45.0( 1 Vote )

# How many terms of

Formula used.

Sn = [2a + (n–1)d]

d = an + 1–an

S20 = 990

a = 2

d = an + 1–an

= 7 – 2 = 5

Sn = [2×2 + (n–1)5]

990 = [4 + 5n–5]

990 = [5n–1]

990×2 = 5n2–n

5n2–n–1980 = 0

n = n can be 20 or –19.8

Since, the number of terms cannot be negative

Sum of 20 terms gives the sum of 990

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