Question:
The first and last terms of an AP are 1 and 11 respectively. If the sum of its terms is 36, find the number of terms.
Solution:
Given: the sum of its terms is 36, the first and last terms of an AP are 1 and 11.
To find: the number of terms
Sum of AP using first and last terms is given by
$\mathrm{S}_{\mathrm{n}}=\frac{\mathrm{n}}{2}(\mathrm{a}+\mathrm{l})$
$36 \times 2=\mathrm{n}(1+11)$
$\mathrm{n}=6$