Solve problems using models involving addition or subtraction of decimal numbers
Using models
Models help us imagine we are trying to work out with number problems. When we work with decimals using grids that are broken into tenths and hundredths, we can count the squares to help us solve our number problems. If we imagine a square is $1$1 unit, we can break it into $10$10 equal rows or columns to represent tenths. We can break it further into $100$100 squares to represent hundredths.
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Let's see how this can help us with the addition of decimals in Video 1.
Subtraction with models
Now let's look at how we can use models to help us subtract decimals. Using a strategy to work through them, rather than guessing, helps us check our understanding.
10 hundredths is equivalent, or has the same value, as 1 tenth.
Worked examples
Question 1
If the whole grid is equal to one whole, how much do the shaded parts add up to? Give your answer as a decimal.
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Question 2
The whole grid is equal to one whole, and we want to subtract $0.28$0.28 from the amount showing.
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First, let's work out what the shaded part is equal to. Give your answer as a decimal.
Now we can solve $0.36-0.28$0.36−0.28, giving your answer as a decimal.
Question 3
Use the blank decimal grid to work out $0.2+0.03$0.2+0.03, giving your answer as a decimal.
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