The 5th term of an AP is – 3 and its common difference is

Foundation

Mathematics Foundation

Sum of n terms of an AP

Question

The 5th term of an AP is – 3 and its common difference is – 4. The sum of its first 10 terms is

– 50

– 30

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a + 4d = – 3 and d = – 4. So, a = 13.

$∴ S_{10} = \frac{10}{2} [2 a + 9 d] = 5 [2 \times 13 + 9 \times (- 4)] = - 50$