Page 143 - Cambridge Checkpoint Mathematics Coursebook 7_Slide

14.3 Using direct proportion

b Weight of chicken for 4 people: 800 g
Weight of chicken for 2 people: 800 g ÷ 2 = g
Weight of chicken for 6 people: 800 g + g = g

7 Bo is paid $65 for 10 hours work. How much does she earn when she works for:
a 5 hours b 15 hours?
8 A catering company charges $960 for a meal for 120 people.
How much do they charge for a meal for:
a 60 people b 300 people?
9 This is part of Li-Ming’s homework.

Question A recipe for 6 people uses 300 g of rice.
How much rice is needed for 15 people?

Solution The recipe is for 6 people, 6 + 9 = 15
6 people need 300 g of rice
3 people need 300 g ÷ 2 = 150 g rice
6 + 3 = 9, so 300 + 150 = 450 g
Altogether 450 g of rice is needed.

Explain what she has done wrong and work out the right answer.
10A teacher orders homework books for her class of 30 students.
The total value of the order is $135.
Two more students join her class, so she orders two extra books.
What is the total value of the order now?

Summary

You should now know that: You should be able to:
★ A ratio is a way of comparing two or more ★ Use ratio notation.
numbers or quantities. ★ Write a ratio in its simplest form.
★ The symbol : is used to show ratio. ★ Divide a quantity into two parts in a given ratio.
★ To write a ratio in its simplest form you divide ★ Recognise the relationship between ratio and
both the numbers by the highest common factor. proportion.
★ To share in a given ratio you need to: ★ Use direct proportion in context.
1 fi nd the total number of parts ★ Solve simple problems involving ratio and direct
2 fi nd the value of one part proportion.
3 fi nd the value of each share. ★ Understand everyday systems of measurement
★ Two quantities are in direct proportion when their and use them to calculate.
ratios stay the same as the quantities increase or ★ Solve word problems involving whole numbers,
decrease. money or measures.

14 Ratio and proportion 141