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Q: What is the sum of the first fifteen counting numbers?

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The sum of first 20 counting numbers is 190.

What is the sum of the first fifteen counting numbers?

The sum of the first 500 odd counting numbers is 250,000.

The sum of the first 50 counting numbers, excluding zero, is 1,251.

The sum of the first 1,000 counting numbers (which excludes zero) is 500,001.

It is 155 greater.

The sum of the first 15 odd numbers is 225.

The sum of the first six counting numbers (1-6) is 19.

Their sum is 328.

The sum of the first 100 counting numbers (1-100) is 5,001.

The sum of the first 10 counting numbers (1-10) is 51.

The sum of the first 500 counting numbers (1-500) is 125,001.

4990

thousands

55

210

The sum of the first 500 even numbers, excluding zero, is 250,500.

Their sum is 10000.

I assume you mean the first three "counting" (ordinal) numbers, which are 1, 2, and 3. The sum is therefore 1 + 4 + 9 = 14.

Yes, the sum of any three consecutive counting numbers has a factor of 3.

The sum of the numbers from 1 to 20 inclusive is 220.

155

1+1+1+1+1+=5 * * * * * The question did not ask for the sum of the first counting number five times! The sum of the first 5 counting numbers is 1+2+3+4+5 = 15. Such sums are known as triangular numbers.

21

Here is a nice way to see and remember this. Look at the sum of the first 5 counting number Write them as 1,2,3,4,5 Now write them backward as 5,4,3,2,1 Place the second list under the first list and add the numbers in each column. Each sum is 6 and there are 5 sums. However, you counted the numbers twice since you wrote the list both ways. So the sum of the first 5 numbers is 5x6/2 In general the sum of the first n natural numbers is n(n+1)/2 So the sum of the first 100 numbers is 100x101/2=50x101=5050 This formula can also be proved by induction and several other ways.