Activity 3.2b

Math Activity 3.2b: Whole Number Subtraction with Base-ten Blocks

Purpose: To explore multiple models for whole number subtraction using base-ten blocks.

Materials: Base-ten blocks or Math Learning Center App Links to an external site. or Cool Math 4 Kids App Links to an external site..

The two main models for subtraction of whole numbers are "Take-Away" and "Comparison".

A model helps you ask and answer a question:

36 - 23 means, what do you get if you take 23 away from 36?

So, start with 36:

Now, take away 23:

That leaves 13!

If we use a different model, then we get a different question.

Julia has $36 and Ruby has $23. How much more does Julia have?

Here we are comparing what the girls have, and no one is taking any thing from any one.

Start by showing each value:

Next line them up to see how they are alike and how they are different:

Now, we can see that Julia has 13 more than Ruby.

So, 36 - 23 = 13.

Now you get to try the same thing with the follow subtraction problems:

1.  47 - 24 
   
   
2.  32 - 17 
   
   
3.  31 - 14 

For each of these,

1. Write a story for the subtraction as a take away, and illustrate the solution with base-ten blocks.
2. Write a story for the subtraction as a comparison, and illustrate the solution with base-ten blocks.

Here is another example where we have to do some trading:

Boe has 35 Lego blocks and Appa has 27. How many more does Boe have?

Since Boe does not have enough singles we will need to trade 1 ten for 10 ones.

Now we can line the like blocks up:

It seems that Boe has 8 more blocks than Appa.

Show your algorithm:

Does your illustration show the borrowing that happened here? It should.

Here is an example built in the Math Learning Center App Links to an external site..