Lesson Guide
Explanation
Money is the decimal you already understand. There are 100 cents in a dollar, which makes one cent one hundredth of a dollar — exactly 0.01. That is the whole reason prices are written with two digits after the point: the first is ten-cent pieces, the second is single cents. Every price tag you have ever looked at was a two-place decimal, so you have been reading these for years without calling them that.
Your Turn
How many cents in half a dollar, and how would you write it? Check: 50 cents, written $0.50.
Watch Out
Two decimal places for money, always. $4.5 is not wrong maths, but on a price tag it should be $4.50.
Explanation
In $6.35 the 6 is six whole dollars. The 3 sits in the tenths column, which for money means three ten-cent pieces, or 30 cents. The 5 sits in hundredths, so five single cents. Put the last two together and you say thirty-five cents. Money is the one place where you read the two decimal digits as a pair rather than separately, because thirty-five cents is how people actually talk — but underneath they are still tenths and hundredths.
Your Turn
In $2.08, how many cents beyond the 2 dollars? Check: 8 cents — the 0 means no ten-cent pieces.
Watch Out
$2.08 is 8 cents, not 80. The zero holds the ten-cent column empty.
Explanation
To turn cents into dollars, count back two places from the right and put the point there — because 100 cents make a dollar. So 275 cents becomes $2.75. If there are no whole dollars you still need a 0 before the point: 40 cents is $0.40. And 5 cents is $0.05, where the zero after the point is doing real work holding the ten-cent column empty. Write $0.5 and you have said 50 cents by mistake.
Your Turn
Write 130 cents and 7 cents as dollar amounts. Check: $1.30 and $0.07.
Watch Out
5 cents is $0.05. Writing $0.5 turns 5 cents into 50 cents — a ten-fold error.
Explanation
Adding money is the written addition you already know, with one rule: line up the decimal points. Then the cents columns sit above each other and everything behaves normally. For $4.75 plus $2.60, the cents give 135, which is more than 100 — so you write 35 and carry one whole dollar, exactly the way ten ones carry into the tens column. The point in the answer goes straight below the points above it.
Your Turn
Work out $3.40 + $1.85 by lining up the points. Check: $5.25.
Watch Out
Lining up the right-hand ends instead of the points is what breaks these. $4.5 + $2.60 must be written as $4.50 + $2.60.
Explanation
Change is subtraction, and you can do it two ways. Set it out and subtract, remembering to write $10 as $10.00 so the columns line up. Or count up from the price to the amount paid, which is the method shopkeepers use and the same counting-up strategy you learned in Year 3: 5 cents gets you to $6.50, another 50 gets you to $7, then $3 more gets you to $10 — total $3.55. Both give the same answer, so doing one and checking with the other is a genuinely good habit.
Your Turn
You pay $20 for something costing $12.70. What is your change? Check: $7.30.
Watch Out
Write $10 as $10.00 before subtracting. Missing columns are where change goes wrong.
📌 Key Points — this lesson in a nutshell
- 100 cents in a dollar, so one cent is 0.01 of a dollar.
- Prices always show two decimal places: ten-cent pieces, then single cents.
- $0.05 is 5 cents; $0.5 is 50 cents. The zero matters.
- To add or subtract, line up the decimal points and fill missing places with zeros.
- Change can be found by subtracting or by counting up — use one to check the other.
Step 1: Introduction
Step 1 of 5
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