Find the sum of all three digit natural numbers, which are divisible by 7.

Explanation

Smallest three digit number divisible by `7 = 105` and the largest `= 994`

`An = 994`

`A = 105`

`D = 7 `

`n= ?`

`An = A + [ n - 1] D`

thus

`994 = 105 + [ n - 1 ] 7`
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