Money and Decimals
Money and decimals go hand-in-hand
When we use dollars and cents, we are really using decimals:
- $1.00 = one whole dollar
- $0.10 = ten cents (one tenth)
- $0.01 = one cent (one hundredth)
Reading and Writing Decimals Using Money
- $2.35 is read as two dollars and thirty-five cents
- $0.75 is read as seventy-five cents
- $4.00 is read as four dollars (no cents)
The digits after the decimal point show:
- tenths → 10¢ coins
- hundredths → 1¢ coins
Example: 65 cents
Is written as $0.65, which can be thought of as:
- 6 lots of 10¢
- plus 5 lots of 1¢
But many other combinations of coins can be used, can you think of some?
Comparing and Ordering Money Amounts
We can compare money amounts by:
- looking at the dollar amount first
- then comparing the cents
Concrete materials like coins or visual models make this easier.
Example: which is less, $0.45 or $0.53?
Both amounts have 0 dollars, so let's just look at the cents.
45 is less than 53, so $0.45 is less than $0.53
Example: which is less, $3.45 or $2.53?
One has $3.00, the other has $2.00.
2 is less than 3, so $2.53 is less than $3.45
We don't need to check the cents.
Example: which is less, $0.90 or $0.09?
Money uses two digits after the decimal point:
| Dollars | . | Tenths (10¢) |
Hundredths (1¢) |
|---|---|---|---|
| 0 | . | 9 | 0 |
| 0 | . | 0 | 9 |
$0.90 is 90 cents. $0.09 is 9 cents. 9 is less than 90 so $0.09 is less than $0.90
See ordering decimals for more.
We can also order amounts from least to greatest:
- $0.30
- $0.08
- $0.65
Ordered from least to greatest:
$0.08, $0.30, $0.65
Multiplying Decimals by a Whole Number (Money)
To multiply money, we can multiply it as a decimal.
Example: a drink costs $1.25. What's the cost of 4 drinks?
Example: a pen costs $0.75. What's the cost of 6 pens?
Note: We keep two digits after the decimal point for money, so we write $4.50, not $4.5.
Example: a sticker costs $0.08. What's the cost of 9 stickers?
Example: $2.35 × 4
Ignore the decimal point for now and multiply as whole numbers.
Let's arrange the places vertically this time:
235
× 4
940
Answer:
$9.40
Calculating Total Cost Using Coins and Dollars
To add money, we can add it as a decimal.
Example
You buy:
- a sandwich for $3.40
- a juice for $1.65
Add the amounts:
$3.40
$1.65
$5.05
Total cost: $5.05
See adding decimals for more.
Try It Yourself
- Write $2 and 7 cents as a decimal
- Which is greater: $0.90 or $0.09?
- Find the cost of 6 items at $0.75 each
- Add these amounts: $4.25 and $2.80
Money gives decimals meaning we can see and use every day.