Question -
Answer -
The series of integersdivisible by 7 between 50 and 500 are 56, 63, 70, …, 497
Let the number ofterms be ‘n’
So, a = 56, d = 63-56= 7, an = 497
an = a+ (n-1)d
497 = 56 + (n-1)7
497 = 56 + 7n – 7
7n = 497 – 56 + 7
7n = 448
n = 448/7
= 64
By using the formula,
Sum of n terms, S =n/2 [a + l]
= 64/2 [56 + 497]
= 32 [553]
= 17696
∴ The sum of allintegers between 50 and 500 which are divisible by 7 is 17696.