It is called *compatible numbers*.

Compatible numbers are numbers that look nice or friendly with each other when we do mental calculation to estimate a product, but especially a division.

Some examples of compatible numbers when doing division are 400 and 10, 36 and 6, 2400 and 12, and 64 and 8:

- 2400 and 12 are compatible because when doing this division (2400/12), we can quickly divide 24 by 12 to get 2 and put two zeros at the end to get 200

Some examples of compatible numbers when doing multiplication are 200 and 40, 1100 and 40, 25 and 4:

- 1100 and 40 are compatible because we can quickly do this multiplication by multipling 11 and 4 to get 44 and add three zeros at the end to get 44000.

Tip! If you're trying to find the percent of a number, it may be helpful to use compatible numbers to find an estimated answer. Follow along with this tutorial to see how to use compatible numbers to estimate the percent of a number from *Virtualnerd.com*.