An A.P has 21 terms. If its 11th term is 25,find the sum
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Answered by
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Step-by-step explanation:
21 terms
a11 = 25
a + 10d = 25
a = 25 - 10d
S21 = n/2 ( 2a + (n - 1) d )
= 21/2 ( 2( 25 - 10d ) + (21- 1) d )
= 21/2 ( 50 - 20d ) + 20d
= 21/2 × 50 - 20d + 20d
= 21 × 25
= 525
Answered by
1
Answer:
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