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Grade 2 · Subtraction

School-fair tickets: subtract from a larger collection

At a school fair, 149 tickets are available and 16 are taken away. 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
School-fair tickets: subtract from a larger collection. Removed so far: 0. Left now: 149. Left at the end: 133149 − 0 = 1490149149left nowRemaining + removed = the original whole.
The quantities are invented for this investigation. Controls change the model rather than real-world records. Displayed decimals are rounded; whole-number counts are exact.

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.

Removed so far
0
Left now
149
Left at the end
133

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.

At a school fair, 149 tickets are available and 16 are taken away. Subtraction separates an original whole into the removed part and the remaining part. The remaining quantity must be counted after the removal, not by recounting the crossed-out objects. At the end, 133 remain. Adding back the removed 16 reconstructs the original 149.

A relationship to keep

149 − 16 = 133

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

    At a school fair, 149 tickets are available and 16 are taken away. Identify what each number measures before changing a control; the worked example refers to these starting values.

  2. STEP 2

    Follow the mathematical change

    Move the timeline to increase the removed amount. The pale or crossed-out section records what has left; the colored section records what remains. Pause on an intermediate frame and compare the picture with the live readouts.

  3. STEP 3

    Explain and test the relationship

    At the end, 133 remain. Adding back the removed 16 reconstructs the original 149. Change one input, predict its effect, and test whether the same relationship still works.

Your turn to explain

Make a prediction. Test your reasoning.

School-fair tickets: use the original situation. At a school fair, 149 tickets are available and 16 are taken away. Return one removed object when possible. What remains then?

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

Compare your explanation

134 remain: 149 − (16 − 1) = 134.

Work through a full lesson

Connect the animation to a worked example and practice questions.

Grade 2 · Algebra

Exchange a ten to subtract

Rename a ten as ten ones before subtracting.