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Grade 4 · Decimals

Food-bank packing: keep cents aligned when adding money

An illustrated budget for a food-bank packing station has costs of $3.20 and $1.50. Change the controls and explain what the animation reveals.

Predict what will happen, press Play, then pause and explain what changed. Every control also works without playback.

Watch the relationship

Paused
Food-bank packing: keep cents aligned when adding money. First amount: $3.20. Added so far: $0.00. Current total: $3.20$3.20 + $0.00 = $3.200$4.70$3.20combined so farKeep the first part; add only the part that arrives.
Prices are fictional and stated in dollars with 100 cents per dollar. No tax, discount, payment, or purchase is included. All arithmetic is performed using integer cents.

Starts paused. Play once, pause anywhere, or use Step to inspect the mathematics. Playback stops when this panel leaves the screen.

Make it your experiment

Change one value. Notice what follows.

The controls adjust the model. Numbers below describe the current frame. Decimals are rounded.

First amount
$3.20
Added so far
$0.00
Current total
$3.20

HD animation studio

From experiment to screen.

Present a crisp Canvas scene, save a full-HD image, or capture your model as a silent video.

Understand what you are seeing

The idea behind the motion.

An illustrated budget for a food-bank packing station has costs of $3.20 and $1.50. Represent both costs in cents before combining them. One hundred cents is one dollar, so the decimal point records place value rather than acting as punctuation between unrelated whole numbers. The planned total is $4.70. This is an invented learning budget with no transaction or purchase attached.

A relationship to keep

320 cents + 150 cents = 470 cents

Read the symbols alongside the explanation. A diagram shows the relationship; the assumptions tell you when it applies.

  1. STEP 1

    Read the starting situation

    An illustrated budget for a food-bank packing station has costs of $3.20 and $1.50. Identify what each number measures before changing a control; the worked example refers to these starting values.

  2. STEP 2

    Follow the mathematical change

    Watch the second cost join the first. Read the same current amount in dollars and cents; every whole dollar contains exactly one hundred cents. Pause on an intermediate frame and compare the picture with the live readouts.

  3. STEP 3

    Explain and test the relationship

    The planned total is $4.70. This is an invented learning budget with no transaction or purchase attached. Change one input, predict its effect, and test whether the same relationship still works.

Your turn to explain

Make a prediction. Test your reasoning.

Food-bank packing: use the original situation. An illustrated budget for a food-bank packing station has costs of $3.20 and $1.50. If the second cost rises by 5 cents, what is the revised total?

Use the values specified in the question. Reset restores the initial values for this investigation.

Compare your explanation

$4.75, because the total increases by exactly $0.05.

Work through a full lesson

Connect the animation to a worked example and practice questions.

Grade 4 · Algebra

Add tenths and hundredths together

Align decimal places when adding two-place decimals.