[header] How to add a consecutive series of numbers in your head [title] Imagine the numbers. [step] Let's suppose that you want to add all the numbers from 1 to 100 in your head. Imagine that on a table in front of you you have arranged stacks of pennies, in a long neat row left to right, to equal each of these numbers. 
For example, the first stack of pennies starting on the left side of the table is just one penny by itself. Beside it, to its right is a stack of 2 pennies.