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.