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What is the sum of the first 9 terms of an arithmetic progression if the first term is 7 and last term is 55?
Answer & Solution
Correct Answer:
Option
B
$$\eqalign{
& {S_n} = \frac{n}{2}\left( {a + l} \right) \cr
& {S_9} = \frac{9}{2}\left( {7 + 55} \right) \cr
& {S_9} = \frac{9}{2} \times 62 \cr
& {S_9} = 9 \times 31 \cr
& \,\,\,\,\,\,\,\,\, = 279 \cr} $$
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