4,203

11

4

This is a simple trick that is rarely taught in school. It is an easy way to divide any number by 5 using mental math. The number does not have to be divisible by 5, it works with any number. I use this trick if I am trying to calculate a 20% tip for a bill since 20% = 1/5.

### Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

## Step 2: Example

Basically, double the number and move the decimal point to the right or vice versa. If you're not good at doubling numbers, split the number up as shown in the next step.

## Step 3: Extra: Doubling

Doubling large numbers in your head is easier when done this way. All you need is some well trained short term memory.

## Recommendations

• ### Lamps Class

9,739 Enrolled

## 4 Discussions

This does seem easier than figuring out 10%, dividing it in half and then adding them together (my usual method). Nice.

I tried it! Pretty cool.
For tips I tend to just double the tax. Of course tax rates vary so this is a neat method to remember.