Question

Find the sum of all natural numbers between
100 and 1000 which are multiples of 7. ​

Answer 1

Answer:

70336

Step-by-step explanation:

your answer is given in the picture above

Answer 2

The first no. after 100 divisible by 7 is 105 & last before 1000 is 994

thus,

a = 105

l = 994

d = 7 ( common difference )

n = ?

From 994 , n can be obtained.

an = a + ( n - 1 )d

994 = 105 + ( n - 1)7

994 - 105 / 7 = n - 1

127 = n - 1

n = 128

Sum of 128 terms = n/ 2 ( a+ 1 )

= 128 / 2 ( 105 + 994 )

= 64 × 1099

= 70336

Answer = 70336