Mental Math Tricks to Impress Your Friends

How to multiply any two digits number by 11

Example:

Square any two digits number that ends with 5

Multiply any two digits numbers with the same first digit and the second digit that sums up to 10

Note that if the product of the second digits is below ten, you have to add a 0 in front of it.

Multiply by 9

To multiply by 9, simply multiply by 10 and then subtract the number itself.

Quickly find percentages

To find out the 15% of a number, divide it by 10 and the add half of it.

To find out the 20% of a number, divide it by 10 and multiply the result by two.

To find out the 5% of a number, divide it by 10 and the divide it by two.

Addition

Left to right approach

Instead of using a right to left approach, we can start from the left and move to the right. Take the following example:

If you’re working with three digits numbers, the process is the same.

Subtraction

Using complements to simplify subtractions even more

Multiplication