The idea in brief. A complement is the amount needed to reach the stated whole-dollar target. One dollar is 100 cents. Keep dollars and cents in their own places. In the lesson. In Primary 2, you wrote money in dollars and cents. Here are ten ten-cent coins. Ten times ten cents is one hundred cents. One hundred cents is one dollar. We will find the money needed to make a whole dollar amount. Keep dollars and cents in their own places, and rename across the zeros.
Lesson video, with the working
Making a whole dollar amount
5 min 52 s
The film teaches 3 questions in turn. Each question shows first; its working is written as the film explains it.
How do you work through how much more money questions in P3?
This page teaches your child to find how much more money makes a whole dollar amount, such as from 45 cents to $1 or from $4.60 to $10.
What your child learns here
This page teaches your child to find how much more money makes a whole dollar amount, such as from 45 cents to $1 or from $4.60 to $10. It applies the P3 outcome on adding and subtracting money in decimal notation, and leans on the fact that 100 cents make 1 dollar.
Know that 1 dollar is 100 cents, and write $1 as $1.00 before subtracting.
Subtract the amount already there from the whole-dollar target to find the amount needed.
Rename across zeros, for example $10.00 as $9 and 100 cents, before subtracting the cents.
Count on as a mental check: from $4.60 to $5 is 40 cents, then $5 more reaches $10, so $5.40 is needed.
Include every note and coin already collected before finding the shortfall.
Does the answer make sense?
Added to everything already collected, the amount needed must reach the whole-dollar target exactly, so its cents and the cents in the total collected make one dollar, unless both are zero. Your child can also check that the amount needed is less than the target, since some money is already there.
How to practise these questions
The Basic question practises making $1 from an amount in cents. The Intermediate questions add making other whole dollar amounts from dollars and cents. The Challenge questions ask your child to fill a gap of both dollars and cents in one go, counting on to the next dollar first. If making a whole dollar is stuck, view that question's solution film and try again later from Revision.
Questions parents ask
Is money in the Primary 3 syllabus? Yes. The Primary 3 MOE syllabus lists adding and subtracting money in decimal notation under Money. Finding how much more makes a whole dollar amount is one use of that subtraction, and it practises renaming 1 dollar as 100 cents.
Should my child count on or subtract to find the money needed? Both are useful. Counting on with coins is a natural way to find the amount needed, and the written subtraction is what the lesson sets out. Doing one and checking with the other builds confidence in the answer.
Why is $10.00 minus an amount harder than other subtractions? The zeros mean there is nothing to subtract from in the cents places, so 1 dollar has to be renamed as 100 cents first. The lesson on this page walks through renaming across the zeros one place at a time.
