Is your learner struggling with subtraction? One of the reasons subtraction is so challenging is that there are many different ways to think about it. If kids lack a strong grounding in number sense and subtraction, they’ll find advanced math and problem solving skills development more difficult.
Yesterday, How to Help Your Child Learn Subtraction, Part One covered subtraction as takeaway, difference, and counting back from (also known as counting down to). Today, we’ll discuss subtraction as regrouping, borrowing or carrying over as well as offer tactics you can use to help your child learn this core arithmetic concept.
Regrouping, Borrowing, or Carrying over
Regrouping, borrowing, or carrying over all refer to taking one set of tens and turning it into ten sets of ones. Or a set of hundreds and turning it into ten sets of tens and so on through the different place values of a given number. Discussing this idea with your child in the same language he or she uses in school will minimize confusion due to word choice.
The idea of regrouping, borrowing, or carrying over relies on understanding our base-10 number system, which is why place value is so critical for learner’s comprehension. (See Motion Math Zoom, a math game focusing on place value, which takes learners on adventures from the thousands place to the thousandths place).
When learners are faced with a subtraction problem such as 952-219, the numbers are too large for them to count back from or count down to. They can think of it as takeaway or difference, but they might not have the best mental model for coming to a concrete answer, especially given the size of the numbers they’re subtracting.
However, if they can approach the problem with regrouping, borrowing, or carrying over, they can subtract each of the ones, tens and hundreds places by counting back from or counting down to. As your learner becomes more fluid with mental math, they may also think of subtracting each of the ones, tens and hundreds places as takeaway and difference.
Let’s look at the example problem, 952-219. We have 9 hundreds, 5 tens, and 2 ones that we’re subtracting 2 hundreds, 1 tens and 9 ones from – let’s visualize this:
Looking at the problem above, we can regroup, borrow or carry over 1 tens from the 5 tens to make the 2 ones into 12 ones – like so:
So now the problem asks us to subtract 9 ones from 12 ones; 1 ten from 4 tens; and 2 hundreds from 9 hundreds — much easier.
If your child is struggling with subtraction you can:
What are your tips or thoughts on what to do if a child is struggling with subtraction? Let us know in the comments – we’d love to hear from you!