Learn with Amar
Teaching video
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Browse grades and teaching videos01 · Read and understand
What you will learn
- Add amounts by matching decimal places.
- Subtract the total from the payment.
- Verify addition with an inverse calculation.
Before you start
Add and subtract whole numbers, including regrouping; identify tenths and hundredths.
Keep paper nearby. Read the question once for the context, then again to identify what is known and what you need to find.
Start with a question
Three fictional supplies cost $2.35, $4.80, and $1.95. What is the total, and how much change should come from $20?
Why this math matters
Money gives decimal places a concrete meaning: one hundredth of a dollar is one cent. Aligning equal-sized units makes addition reliable, while an estimate can reveal a misplaced decimal before it reaches a final answer.
Set up the model
A useful answer starts with clear assumptions:
- The fictional prices already include every charge.
- The payment is exactly $20, and all amounts are exact to the cent.
02 · Work through the example
Follow the reasoning, one step at a time.
Try to predict the next step before reading it. After each calculation, explain why the operation makes sense and how it helps answer the original question.
Work through it with Amar
See this example unfold.
The complete worked example, one idea at a time.
Add a shopping total with decimal place value
PausedQuestion: Start with the question. Paused.
Question
Start with the question
Three fictional supplies cost $2.35, $4.80, and $1.95. What is the total, and how much change should come from $20?
Before you calculate
Read what is known and what you need to find. Make a prediction before moving to the first calculation.
Starts paused. Play advances through the full text at a reading pace; pause whenever you need more time. Previous, Next, and the phase buttons let you set your own pace. Playback pauses when this walkthrough leaves the screen or you switch tabs.
Your device’s reduced-motion setting keeps each phase still. Manual controls remain available. The full written solution stays below.
Match the units
$4.8 = $4.80; 235 + 480 + 195 cents
Writing two decimal places makes the cents explicit. An added trailing zero changes the notation but not the amount.
Find the exact total
235 + 480 + 195 = 910 cents = $9.10
Alternatively, align the decimal points and add the columns. A nearest-dollar estimate of 2 + 5 + 2 = 9 supports the result's scale.
Find and verify the change
$20.00 − $9.10 = $10.90; $9.10 + $10.90 = $20.00
Adding the change back to the cost reverses the subtraction. This checks the transaction without relying on the original subtraction alone.
The result
The total is $9.10 and the change is $10.90.
The final zero in $9.10 shows cents clearly. It is the same numerical amount as $9.1, but currency formatting reduces the chance that a reader confuses cents and tenths.
Common mistakes to catch
- Align decimal points, rather than the rightmost written digits.
- Do not round individual prices to dollars before finding an exact total.
03 · Practice independently
Try it before revealing the answer.
Use paper or a calculator as needed. Write your units and reasoning, then open the hint or explanation to check your approach.
Practice 1
Add $3.75, $2.60, and $0.85.
Show a hint
The first and last prices sum to a convenient amount.
Reveal answer and explanation
$7.20
$3.75 + $0.85 = $4.60, and $4.60 + $2.60 = $7.20.
Practice 2
Four notebooks cost $1.25 each, and a folder costs $2.40. Find the total.
Show a hint
Find the notebooks' cost before adding the folder.
Reveal answer and explanation
$7.40
4 × $1.25 = $5.00. Adding $2.40 produces $7.40; the folder's price is added only once.
Take the idea with you
Write the same purchase calculation entirely in cents, then in dollars. Explain why the two approaches agree.
04 · Reflect and continue
Can you explain it in your own words?
Before moving on, explain the main idea without looking at the worked example. Try both practice questions, check your reasoning, and name one mistake you now know how to avoid. Return to a step if you still need support.
Up next: Combine recipe amounts with unlike fractions
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