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

Sure, let's solve this step by step.

Step 1: Identify the first and last three-digit numbers that are divisible by 7.

The first three-digit number divisible by 7 is 105 (715), and the last is 994 (7142).

Step 2: Use the formula for the sum of an arithmetic series.

The formula is: Sum = n/2 * (a + l) where n is the number of terms, a is the first term, and l is the last term.

Step 3: Calculate the number of terms (n).

The number of terms is the last term divided by 7 minus the first term divided by 7 plus 1. So, n = 142 - 15 + 1 = 128.

Step 4: Substitute the values into the formula.

Sum = 128/2 * (105 + 994) = 64 * 1099 = 70336.

So, the sum of all three-digit natural numbers, which are divisible by 7, is 70336.