Ratios | Substitute Teacher
Students learn what ratios are and how they are used in computer science to compare quantities, such as screen sizes, data parts, and mix ratios in simple coding or design tasks. The lesson is designed for a substitute teacher and uses simple, low-prep activities with clear examples.
| Term | Definition |
|---|---|
| ratio | A comparison of two quantities. |
| part-to-part | A ratio that compares one group to another group. |
| part-to-whole | A ratio that compares one group to the total. |
| simplify | To make a ratio easier to understand by dividing both parts by the same number. |
Write 2 simple comparisons on the board, such as 3 cats to 6 dogs and 2 blue pixels to 8 red pixels. Ask students what is being compared and how they are alike.
Share ideas, notice that both examples compare two amounts, and respond to questions.
Explain that a ratio compares two quantities. Model writing ratios as 3:6, 3 to 6, and 3/6. Show a computer science example such as 2 green blocks for every 5 blue blocks in a design.
Listen, repeat the examples, and copy the notes.
Work through 3 examples together on the board. Ask students to identify the two parts being compared and write each ratio in a chosen form.
Solve with the teacher and answer aloud or on paper.
Give students 4–5 simple ratio prompts related to computer science, such as pixels, icons, app buttons, or code blocks. Circulate and help as needed.
Independently or with a partner, write the ratio for each prompt and simplify when possible.
Review answers as a class. Ask volunteers to explain one problem and how they found the ratio.
Check their work and share solutions.
Ask students to complete a quick exit question: Write one ratio from today and explain what it compares.
Submit a short written response before leaving.
Review that a ratio compares two quantities and can be written in different ways. Ask students to name one place ratios might appear in computer science, such as images, buttons, or code blocks.
Students will be assessed through guided practice responses, the independent activity, and the exit check response.