Question

Find the sum of the integers between 50 and 500 which are divisible by 7

Answer 1

The required A.P is 56,63,70,77,....497
Here a=56
d=7
we have
nth term=1st term+(n-1)d
497=56+(n-1)7
497=49+7n
7n=448
n=64
now sum can be,
S=n/2 (1st term+ nth term)
S=64/2 (56+497)
S=32×553
S=17696
required sum is 17696