Question

The 5th term of an A.P. is $$-3$$ and its common difference is $$-4$$. The sum of its first $$10$$ terms is ______.

Options

• $$-50$$

• $$-40$$

• $$-60$$

• $$-30$$

Answer 1

The 5th term of an A.P. is $$-3$$ and its common difference is $$-4$$. The sum of its first $$10$$ terms is –50.

Explanation:

From $$-3 = a + 4(-4)$$, the first term is $$a = 13$$. 

Thus $$\mathrm{S}_{10} = \frac{10}{2}[2(13) + 9(-4)] = -50$$.