Subtraction using the F-L-U model

Pre-requisites:

• Recognising numbers represented in FLU model
• Representing numbers in FLU model
• Addition with and without carryover using FLU model
• Knowing that when there are >10 units/longs, they must be grouped together and replaced with a long/flat

Learning objectives:

• To understand how the FLU model can be used to perform subtraction of upto 3 digit numbers with and without regrouping
• To visualize what it means to regroup/’borrow’
• To correlate the subtraction process using FLU model to the standard algorithm

Materials: None

Process:

Whole class:

1. Begin the class with a revision of previously discussed concepts – representing numbers using the FLU model, performing addition, grouping 10s

2. Ask students what they understand by subtraction, discuss the meaning and also ask them to explain how they solve it using some examples

3. Explain subtraction using the model taking 2 or 3 examples. Then ask 1 or 2 students to come to the board and explain in the way they understood it

Note: When using the model, the subtrahend(number being subtracted) is mainly written only as a reference to keep track of how much needs to be taken away from the minuend. So, the answer would be whatever is left of the minuend after subtracting only.

Eg – 5-2 is represented as o o o o o

- o o

Here, it’s not just the 2 dots in the 2nd row that need to be taken away but 2 dots from the 5 dots in the 1st row. This needs to be explained very clearly to students. Hence the discussion about the meaning of subtraction becomes very important.

4. Assign 3 problems without regrouping for students to solve.

Problem 1: choose any number between 5 and 10

choose 2nd number between 1 and 4

Subtract the two

Problem 2: Choose any number between 11 and 20, choose 2nd number between 1 and 9, subtract

Problem 3: Choose any number between 15 and 20, choose 2nd number between 10 and 14, subtract

5. Next, write an example problem that involves regrouping ans ask if anyone can try and explain how the model would work in this situation. Use the student responses to explain how the model can be used to perform subtraction involving regrouping. Demonstrate using the Geogebra simulation.

6. Split up students into smaller groups and give a chit to each one of them. Ask them to write any number between 1 and 50 (model representation). In small groups, let students take turns to pick up two chits and subtract the smaller number from the larger one.