The idea in brief. Align dollars with dollars and cents with cents; regroup at 100 cents. Align the decimal points and keep two digits for cents in the answer. In the lesson. In the last lesson, you subtracted money by renaming. Ten ten-cents make one dollar. Today we add and subtract money by lining up the decimal points. Line up the decimal points, and remember that ten ten-cents make one dollar.
Lesson video, with the working
Adding and subtracting dollars and cents
5 min 19 s
The film teaches 3 questions in turn. Each question shows first; its working is written as the film explains it.
How do you set out adding and subtracting money questions in P3?
This page teaches adding and subtracting money written in decimal notation, such as $7.45 and $12.80, which is the P3 Money outcome.
What your child learns here
This page teaches adding and subtracting money written in decimal notation, such as $7.45 and $12.80, which is the P3 Money outcome. Your child sets the amounts out in columns, regroups between cents and dollars, and uses the result in short word problems.
Read an amount like $6.05 as 6 dollars and 5 cents, with two digits after the decimal point for the cents.
Line up the decimal points so dollars sit under dollars and cents under cents.
Add with regrouping: 100 cents make 1 dollar, so 10 ten-cents carry into the dollars.
Subtract with renaming: change 1 dollar into 10 ten-cents when a column runs short.
Choose addition for a total, and subtraction for money left, money needed or a difference.
Does the answer make sense?
If your child rounds each amount to the nearest dollar first, the exact answer should sit within a dollar or two of that estimate. The answer also needs exactly two digits after the decimal point, since those two digits are the cents, so a result with one or three digits there has slipped a column.
How to practise these questions
The Basic question practises adding and subtracting money by lining up the dollars and the cents. The Intermediate questions add regrouping 100 cents into a dollar, or a dollar into 100 cents. The Challenge questions bring in several amounts or a missing amount to be found from a total. When a money sum stalls, play its solution film with your child and return to it later from Revision.
Questions parents ask
Does my P3 child need to know decimals for money? Only as money. The Primary 3 syllabus covers adding and subtracting money in decimal notation, so your child reads $4.35 as 4 dollars 35 cents and lines up the decimal points. Decimals as numbers in their own right come later in the syllabus.
Should my child change dollars to cents before adding? It is one way, but the lesson here keeps the decimal points lined up and regroups 10 ten-cents as 1 dollar. Either method gives the same answer, and the column method keeps the working short.
How can I help my child line up the decimal points? Squared paper helps, with one digit per square and the decimal point on a grid line. Writing the decimal points first, then the digits around them, keeps dollars under dollars and cents under cents.
