Compatible numbers - Definition with Examples

What is Compatible Numbers?

In mathematics, compatible numbers are the numbers that are easy to add, subtract, multiply, or divide mentally.  Compatible numbers are close in value to the actual numbers that make estimating the answer and computing problems easier. 

So, we know the answer is about 1040 or 1000.

Subtraction:

Find the difference between 376.5 and 612.2

Here, we cannot find the difference between 376.5 and 612.2 easily as they are not compatible. So, we make the numbers compatible by rounding both the numbers to the nearest tens.

Actual Difference	Difference using Compatible Numbers
	376.5 changes to 380 612.2 changes to 610   610 - 380 = 230

Multiplication:

Find the product of 24.3 and 18.7.

It is difficult to find the product of 24.3 and 18.7 mentally and quickly. So, we use compatible numbers and find the product which is closer to the actual answer.

Actual Product	Product using Compatible Numbers
	24.3 changes to 24 18.7 changes to 20   24 × 20 = 480

Division:

Divide 856 by 33.

To find the answer to 856 ÷ 33, will take us time as we need to divide to get the answer.

However, if we make the numbers compatible, we can mentally find an answer close to the actual answer as shown,

Actual Division	Quotient using Compatible Numbers
	856 changes to  900  33 changes to 30    900 ÷ 30 = 30