Question

Find the sum of all multiple of 9lying between 400and500

Answer 1

hope this answer will help you.

Answer 2

a=405

d=9

a_n=495

n=11

S_n=

$11 \div 2(2 \times 405 + 10 \times 90)$

$11 \div 2 \times 900$

= 4950

Therefore the sum = 4950