Are you ever faced with a problem where you need to add up a series of numbers? Let’s say for example, you wanted to add up all the numbers between 1 and 10. You could do 1 + 2 +3 +… 10 and try it that way. This won’t be easy for a large series of numbers unless you have a fantastic memory. However, if I lay the number out like this, can you see an easier way?
1 + 10
2 + 9
3 + 8
4 + 7
5 + 6
well, all those number pairs add up to 11, and there are 5 of them. Therefore adding the series of numbers from 1 to 10 equals 55 as we end up having 5 sets of 11. The basic formula for doing this is take the highest number (10) add the lowest number to it (1) then multiply that new figure by half the amount of the highest number (5).
Add all the numbers between 1 and 100.
We get highest of 100 plus the lowest of 1 equals 101. There will be 50 sets, so we do 50 x 101 and arrive at 5050