Find the sum of first 20 terms of an A. P. whose first term is 3 and the last term is 57.

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Solution

Sn = n/2 (a+an)

S20 = 20/2 (3+57)

S20 = 10(60)

S20 = 600

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Find the sum of first 20 terms of an A. P. whose first term is 3 and the last term is 57.

Sn = n/2 (a+an) S20 = 20/2 (3+57) S20 = 10(60) S20 = 600

Sn = n/2 (a+an)

S20 = 20/2 (3+57)

S20 = 10(60)

S20 = 600