Maths • Classes 9–12

Back to the beginning—or not?

A rise and an equal percentage fall do not cancel.

About 20 minutes Read · try · explain

Take your time. Speak, draw or write your answers.

Your list stays in this device’s browser. No name or learner account is needed. Other users of a shared device can see it.

01 / UNDERSTAND

Here is what is happening.

Percentage change depends on the starting value for each step. A model quantity of 100 rises by 20% to 120. A 20% fall from 120 removes 24 and leaves 96. The percentage numbers match, but their bases differ. Always write the base before calculating.

Pause. Make the idea your own.

Explain one idea to a partner, draw it or write it in your own words. Which part is an observation, an example or a question?

You can use a home language. No need to share personal experiences or finish everything in one sitting.

02 / MAKE IT YOUR OWN

Your little investigation

What you need

Paper and a pencil, or a partner to talk with. Drawing and speaking are welcome.

Draw a 100-unit bar and add 20 units.
Find one fifth of the new total and remove it.
Explain why subtracting 20 at the second step would answer a different question.

03 / CHECK YOUR UNDERSTANDING