Sequence Sums

This shortcut helps you add numbers that are evenly spaced in a sequence. To use the shortcut, the numbers must be the same distance apart all the way through the sequence.

Problem: 12 + 18 + 24 + 30 + 36 =  ???? 

Here's how you do it:

1. Add the first and last number. Keep it in your head 48

2. Put your index finger over the first number and your right index finger over the last one.

3. Slide your index fingers in toward the middle of the series, adding the number in your mind to the total each time.

(covering 12 and 36) Think: "48"
(sliding to cover 18 and 30) think "plus 48 = 96"
(sliding to cover 24) think "plus 24 = 120"

For small numbers, this mental addition is really easy to do!