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If in an A.P., first term is 20 and 12^th term is 120. Find the sum up to 12^th term.(a) 420(b) 840(c) 140(d) 1680The question was asked during an internship interview.Question is from Arithmetic Progression(A.P.) in portion Sequences and Series of Mathematics – Class 11

Answer»

Correct CHOICE is (b) 840

To explain: Given, a=20, a12= 120, n=12.

Sn = \(\frac{n}{2}\) (a+l) => S12 = \(\frac{12}{2} (20+120)\) = 6*140 = 840.



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