Question

The first and the last terms of an A.P. are $$1$$ and $$11$$ respectively. If the sum of its terms is $$36$$, then the number of terms is ______.

Options

• $$6$$

• $$7$$

• $$8$$

• $$9$$

Answer 1

The first and the last terms of an A.P. are $$1$$ and $$11$$ respectively. If the sum of its terms is $$36$$, then the number of terms is 6.

Explanation:

$$\mathrm{S}_{n} = \frac{n}{2}(a + l) = \frac{n}{2}(1 + 11) = 6n = 36$$, so $$n = 6$$.