2+4+6+8+、、、+ 100

=(2+ 100)X50/2

=2X50/2+ 100X50/2

=50+2500

=2550

2. The accumulation formula of addition:

n+(n+k)+(n+2k)+(n+3k)+、n+mk

=[n+(n+mk)]*m/2

3. Principles:

The first and last items are averaged and then multiplied by a number, such as 1+2+3+4,, +9, a number ***9, and the sum of the first and last items is equal to 10, and the average value is taken. Multiply the average by 9. Equal to 45. (This seems to be junior high school mathematics)