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Grade 5 · Decimals

Solar-project planning: multiply a decimal price by a count

An invented budget for a model solar-energy project lists 2 identical items at $0.35 each. 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
Solar-project planning: multiply a decimal price by a count. Price per item: $0.35. Current subtotal: $0.00. Final total: $0.702 × $0.35 = $0.70$0.35$0.35Each new card contributes one identical amount.
Prices are invented and use 100 cents per dollar. Counts are whole numbers. Tax, discounts, shipping, and real purchases are outside this mathematical model.

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.

Price per item
$0.35
Current subtotal
$0.00
Final total
$0.70

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 invented budget for a model solar-energy project lists 2 identical items at $0.35 each. A decimal price multiplied by a whole count repeats the same cost. Integer-cent arithmetic avoids losing a place value or treating a decimal point as an instruction to round. The exact total is 70 cents, written $0.70. These are fictional values for learning, not an offer to buy anything.

A relationship to keep

2 × $0.35 = $0.70

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 invented budget for a model solar-energy project lists 2 identical items at $0.35 each. Identify what each number measures before changing a control; the worked example refers to these starting values.

  2. STEP 2

    Follow the mathematical change

    Reveal one item at a time and add its price to the subtotal. Compare the complete subtotal with the product of price and count. Pause on an intermediate frame and compare the picture with the live readouts.

  3. STEP 3

    Explain and test the relationship

    The exact total is 70 cents, written $0.70. These are fictional values for learning, not an offer to buy anything. Change one input, predict its effect, and test whether the same relationship still works.

Your turn to explain

Make a prediction. Test your reasoning.

Solar-project planning: use the original situation. An invented budget for a model solar-energy project lists 2 identical items at $0.35 each. What total would one additional item produce?

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

Compare your explanation

$1.05, adding another $0.35.

Work through a full lesson

Connect the animation to a worked example and practice questions.

Grade 5 · Algebra

Multiply a decimal by a whole count

Use fractional place value to locate a decimal product.