Multiplicative Comparison
Solve word problems involving multiplicative comparison using drawings and equations with a symbol for the unknown number
What a learner can do afterwards
- A blue ribbon is 3 times as long as a red ribbon of 7 cm — how long is the blue ribbon?
- 36 is 4 times a number — what is the number?
- Explain why 'Sam has 5 more' is additive but 'Sam has 5 times as many' is multiplicative
The lesson
You already know that 'times as many' means multiply, not add. Now you will write that idea as an equation, using a letter or symbol to stand for the number you do not know yet.
A red ribbon is 7 cm long. A blue ribbon is 3 times as long. Write it as an equation: 3 x 7 = b, where b is the blue ribbon's length. Solve: b = 21 cm.
The symbol can be a letter like n or a box like this: ▢. Read the equation like a sentence: '4 times a number equals 36' becomes 4 x n = 36.
Turn a 'times as many' problem into a multiplication equation with a symbol for the unknown, then solve for that symbol.
Watch it
Where it sits
This opens up
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.