Solve comparison and change problems using multiplication | Maths

Starter quiz

15 multiplied by 5 is equal to ______
- '75' ✓
40 × 3 = ______
- '120' ✓
Which sentences describe this image?
- The blue ribbon is double the length of the white ribbon. ✓
- The white ribbon is the same length as the blue ribbon.
- The white ribbon is two times the length of the blue ribbon.
- The blue ribbon is two times the length of the white ribbon. ✓
The white ribbon is 18 cm long. How long is the blue ribbon? The blue ribbon is ______ cm long
- '36 cm' ✓
The red ribbon is 11 cm long. Which calculation would you need to do to calculate the length of the white ribbon?
- 11 × 4 =
- 11 × 3 = ✓
- 11 + 3 =
True or false: If the white ribbon is is less than 50 cm long, the blue ribbon will be less than 1 m long.
- True ✓
- False

A 25 cm piece of elastic is stretched to twice its length. Which image represents the problem?
How long is the elastic now that it has been stretched to twice its original length of 25 cm? The elastic is now ______ cm long.
- '50' ✓
A dog is three times the height of a cat. Which bar model represents this?
The cat is 30 cm tall. The dog is three times as tall. The dog is ______ cm tall.
- '90' ✓
Which expression represents the 30 cm tall cat and the dog three times the height?
- 30 cm × 3 ✓
- 3 cm × 30
- 30 cm + 3
Which statement describes this equation: 7 × 8 = 56
- 56 is seven times the value of eight. ✓
- 8 is seven times the value of 56
- 7 is eight times the value of 56
- 56 is eight times the size of seven. ✓

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A change in length can be described using multiplication.
The stem sentence, 'The ___ is ___ times the length of the ___' can be used to compare lengths.
Comparison and change problems can be represented visually to support solving them.

Children may say, 'Tens times taller', which is imprecise.

We say, 'Ten times the original height' because this is more precise and can be used when the scale factor is fractional.

Comparison - When a comparison is made, we are determining how different two objects are. In this case, how many times longer, taller or deeper an object is than another.
Change - A comparison can also be made between an object at the start of, and then after, a change. Examples of change include a change in height of a flower due to growth.