Find the sum of following APs 1) given, 1/15, 1/12, 1/10,... ...., to 11 terms
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Answer:
given : a = 1/15, d = 1/12 - 1/15 = (5 - 4)/60 => 1/60
n = 11
to find a₁₁
Formula used Sₙ = n/2 [2a + (n - 1) d ]
=> S₁₁ = 11/2 [ 2x1/15 + 10 x 1/60 ]
=> S₁₁ = 11/2 [ 2/15 + 1/6 ]
=> S₁₁ = 11/2 [(8 + 10)/60 ]
=> S₁₁ = 11/2 [18/60]
=> S₁₁ = 11/2 x 3/10
=> S₁₁ = 33/60
=> S₁₁ = 11/20
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