Question

how many terms of arithmetic sequence 5 7 9 .....must be added to get 140?

Answer 1

a = 5.
d = 7-5 = 2.
Sn = 140.
Put this values into the following formula.
$sn = \frac{n}{2}(2a + (n - 1)d)$
After solving this,
n = (- 14) and 10.
Neglecting - ve value (no. Of terms can't be negative),
n = 10 terms.




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