How can i use compatible numbers to estimate the quotient of a decimal and whole number?

Well you can use a compatible number is a evein number all the time and u can make it into a hole number is ... wen u frind the number of the compatible number is like 10 or 20 right then u subtract 10 or 20 it all was with 2 then it becomes a decimal so the decimal I will be using 20 and 20-2=18 so into a decimal will become 0.18 and the whole number will be 18