**Question:**I was working in a primary school the other day and i saw the question: "if I add 1+2+3+4 all the way to +1000 what is the answer?" Was this a crucial part of primary I missed?! How do you figure this out?

500,500. It was Karl Gauss's summation formula. n = 1,000 (in this case).

(n/2)*(n+1)= 500 * 1,001 = 500,500.

Why dont you just add them up X Cindy

You figure it out by adding them up, makes the kids think about BIG numbers

You know a bit like the chess board question, put one grain of rice on the first square, 2 on the second, 4 on the third, keep doubling the no. of grains of rice on each square, how many grains go on the last square ?

The formula for that equation as I remember is:

(n/2)*(n+1). N is equivalent to your last number.

If you add up every consecutive number from 1 (one) to 1000 (one thousand) you get a total of 500,500 (five hundred thousand five hundred).

500,500

If the you don't like using the formulas think of it like this...

imagine pairing the numbers up 1000+1, 999+2, you can do this until you get to 501+500, so you end up with 500 x 1001=500,500

500,500

500,500

Let x = 1 + 2 + .. + 1000

Writing the numbers backwards underneath:

x = 1000 + 999 + 998 + ... + 1

(On paper you will be able to line them up vertically in pairs.)

Each vertical pair adds up to 1001.

Therefore when you add these two equations, you get:

2x = 1001 + 1001 + 1001 + . + 1001

There are 1000 terms in the series, and therefore:

2x = 1001 * 1000

Dividing by 2:

x = 1001 * 1000 / 2

= 1001000 / 2

= 500500.

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