Question

Find the sum of all integers between 84 and 179 which is multiplied by 5

Answer 1

The multiples of 5 between 84 to 179

85,90,95,100,................170,175

a=85, d=90-85=5, l or An= 175

An= a+(n-1)d

175=85+(n-1)5

175-85=5n-5

90+5=5n

5n=95

n=95/5=19

Sn=n/2 (a+l)

= 19/2 (85+175)

=19/2 ( 260)

19/2*260

19*130= 2470.