New
New
Year 7

Determining the part

I can determine one part, given the other part and the ratio.

New
New
Year 7

Determining the part

I can determine one part, given the other part and the ratio.

Lesson details

Key learning points

  1. It is not necessary to calculate the total original amount.
  2. Different representations have different limitations.
  3. A bar model can be very effective here.

Common misconception

Always dividing the amount by the sum of the 'parts' of the ratio to get one 'part'.

Offer opportunities to match problems to bar models, ensure the same numbers are used to highlight the differences.

Keywords

  • Proportion - Variables are in proportion if they have a constant multiplicative relationship.

  • Ratio - A ratio shows the relative sizes of 2 or more values and allows you to compare a part with another part in a whole.

Challenge pupils to come up with context questions which do not work. This should help to encourage them to consider the reasonableness of their answers.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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6 Questions

Q1.
How is 6 : 11 read aloud in words?
Correct Answer: 6 to 11
Q2.
What number is represented by the question mark in this bar model?
An image in a quiz
Correct Answer: 48, forty-eight, forty eight, fortyeight
Q3.
Sam and Aisha share some stickers in the ratio of 3 : 5. Aisha gets 25 stickers, how many stickers are there in total?
Correct Answer: 40, 40 stickers, forty, forty stickers
Q4.
Laura, Jacob and Jun share some sweets in the ratio 5 : 6 : 3. Jacob gets 24 sweets, how many sweets are there in total?
Correct Answer: 56, 56 sweets, fifty-six, fifty six, fiftysix
Q5.
Lucas is making necklaces with red, blue and white beads in the ratio 2 : 7 : 5. He uses 15 white beads. How many beads are on each necklace?
Correct Answer: 42, 42 beads, forty-two, forty two, fortytwo
Q6.
The lengths of the sides of a triangle are split in the ratio 3 : 8 : 7. The shortest side is 6.6 cm, what is the perimeter of the triangle?
Correct Answer: 39.6 cm, 39.6, 39.6 centimetres, 39.6 centimetre

6 Questions

Q1.
Complete the sentence: When using a bar model the parts must be .
Correct Answer: equal, the same, the same size
Q2.
What number is represented by the question mark in this bar model?
An image in a quiz
Correct Answer: 8, eight
Q3.
A bunch of flowers contains red and yellow flowers in the ratio 3 : 5. There are 9 red flowers. How many yellow flowers are in the bunch?
Correct Answer: 15, 15 yellow, fifteen, 15 yellow flowers
Q4.
The ratio of flour to butter to sugar in a cookie recipe is 3 : 2 : 1 . You use 180g of flour. How much butter is used?
Correct Answer: 120 g, 120 grams, 120g, 120grams, 120
Q5.
Andeep, Sam and Sofia share some sweets in the ratio 3 : 8 : 5 Sofia gets 20 sweets, how many does Andeep get?
Correct Answer: 12, 12 sweets, twelve, twelve sweets
Q6.
The lengths of the sides of a triangle are split in the ratio 3 : 8 : 7 The longest side is 4.8 cm, what is the length of the shortest side?
Correct Answer: 1.8 cm, 1.8cm, 1.8 centimetres, 1.8centimetres, 1.8 centimetre