Subtraction Confusion – a very simple solution

Do any of your students get in a mess with “double borrowing”? There’s a very simple solution which builds on their existing knowledge of subtraction with borrowing….

Easy subtraction - one "layer" of borrowing
Easy subtraction – one “layer” of borrowing

Much harder subtraction - the borrowing cascades from left to right
Much harder subtraction – the borrowing cascades from left to right and is very likely to go wrong.

There is a very simple solution to this, encourage the student to look at the number differently. Borrow ONCE from the “200” on the top, which becomes 199.

Borrow ONCE from the "200" in the top number
Borrow ONCE from the “200” in the top number – now this sum is ready to do, and there’s far less that can go wrong.

Try it on a student near you, and use the reply box to tell readers what happened next!