Question

The sum of all even numbers between 21 and 51 is –

Answer 1

Series =22+24+26...+50=22+24+26...+50

First even no. = 22

Last even no. = 50

difference = 2

Number of terms

=Last no.−first no.difference+1=Last no.−first no.difference+1

=50−222+1=14+1=15=50−222+1=14+1=15

Sum of 'n' numbers

n2[2a+(n−1)d]n2[2a+(n−1)d]

where 'a' is first no. and 'd' is difference

sum

=152[(2×22)+(15−1)2]=152[72]=152[(2×22)+(15−1)2]=152[72]

15×36=540