find the sum of all 11 terms of an AP whose middle term is 30
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The middle term is the 6th term of the sequence.
6th term = a + 5d, where a = first term and d = common difference
Therefore
a + 5d = 30 ……………(1)
Sum for the eleven terms is given by:
S₁₁ = 11/2[ 2a + 10d] …….(2)
Multiply (1) by 2
2a + 10d = 60 ……………(3)
Substitute (3) into (2)
S₁₁ = 11/2[ 60]
= 330
6th term = a + 5d, where a = first term and d = common difference
Therefore
a + 5d = 30 ……………(1)
Sum for the eleven terms is given by:
S₁₁ = 11/2[ 2a + 10d] …….(2)
Multiply (1) by 2
2a + 10d = 60 ……………(3)
Substitute (3) into (2)
S₁₁ = 11/2[ 60]
= 330
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