The sum of an A.P. is 220 and the first term is 10. If the last term is 30, find the number of terms. Click to Show/Hide Solution \[ S_n = \frac{n}{2}(a_1 + a_{last}) \] \[ 220 = \frac{n}{2}(10 + 30) \] \[ n = 11 \leftarrow \text{answer} \]
