Answer
396
Work Step by Step
Sum even integers between 21 and 45 = 22 + 24 + 26+ 28+........+44
First term $a_{1}$ = 22
Last term $a_{l}$= 44
Common difference (d)= 2
Number of terms = $\frac{(Last term - first term)}{difference (d)}$ + 1
Number of terms (n) = $\frac{(44 - 22)}{2}$ + 1 = $\frac{22}{2}$ + 1 = 11 + 1 = 12
Sum of n terms = $\frac{n}{2}$($a_{1}$ + $a_{n}$)
= $\frac{n}{2}$($a_{1}$ + $a_{l}$)
= $\frac{12}{2}$(22 + 44)
= 6$\times$66
Sum 12 even integers between 21 and 45 = 22 + 24 + 26+ 28+........+44= 396
