8*20 + 8*4 = 160 + 32 = 192.
There are several ways to use compatible numbers, however, so you may find some arithmetic you think is easier.
568-342 using compatible numbers = 226
Estimate 43/81 by using compatible numbers
535.6 divided by 35 using compatible numbers = 15.302857142857144
It is 0.7*600 = 420
The best way to estimate a quotient using compatible numbers is to first understand how compatible numbers work. They are numbers that are close in value to the actual numbers and are easily added, subtracted or divided.
1800
Umm you divide...
231/34
:(
2025.25
6.9877
84.9523