Compatible Numbers (with Division)

Working in a Title 1 school is always an adventure. When I did a model lesson, I introduced the topic and vocabulary word "compatible" with the hook question, "How many of you have seen the advertisements for Match.com (c) ?"

Sure enough students raise their hands and before long began shouting out other dating sites they've seen commercials for! Before long, we began conversations about how they match those who sign up with others who they are compatible with by using their likes and hobbies. From that discussion they were able to ascertain that 'compatible' meant something like 'finding someone who has something in common with you'.

Compatible numbers has been quite the nemesis for teachers primarily because it's a new concept. Before now, we were accustomed to 'rounding' as a strategy to estimate solutions (sums, differences, products and quotients). But compatible numbers is something we, as adults, use in our everyday mental math (believe it or not).

I would explain it as simply finding numbers that work friendly with other numbers.

• In addition & subtraction, 5s and 0s are easier to add (without regrouping) or digits that make ten.
• In multiplication, 0s & 2s are the easiest to mentally multiply.
• Watch this video to see what type of numbers are compatible with divisor in division...