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3.04 Rates in context

Worksheet
Best buys
1

Carol needs 2 planks of wood to complete a cabinet she is going to sell. The planks of wood are sold in packs of 3 for \$40 per pack or in a pack of 10 for \$100 per pack.

a

What is the unit cost for the pack of 3?

b

What is the unit cost for the pack of 10?

c

Based on the unit costs, which is the better buy?

d

In Carol's circumstance, is it worth spending more money to get the cheaper unit cost? Explain your answer.

2

A 500 g bag of almonds usually costs \$12.95 and a 200 g bag of almonds costs \$8.95. Today the 500 g bag is for sale at 10\% off.

a

Find the price per gram of the 500 g bag of almonds after the discount in cents. Round your answer to two decimal places.

b

Find the price per gram of the 200 g bag of almonds in cents. Round your answer to two decimal places.

c

Which bag of almonds is better value in terms of price per gram?

d

What is the difference between the two bags of almonds in terms of cents per gram?

3

2 L of milk, with an expiry date a week from today, costs \$3.00. A large 4 L bottle of the same brand, which expires in two days, is discounted to \$3.40.

a

What is the unit cost of the 2 L bottle?

b

What is the unit cost of the 4 L bottle?

c

Which is the better buy?

d

If a family usually take a week to get through 2 L of milk, is it worth spending more money to get the cheaper unit cost for the family? Explain your answer.

4

A store sells hats for \$ 4 each and offers one free hat for every 6 hats a customer buys.

a

Calculate the average price of one hat for a customer who pays for 6 hats.

b

How much more would a customer wanting to purchase 7 hats have to pay if the special offer did not exist?

Other contexts
5

Adam really likes apples and eats them at a rate of 4 per day.

a

Find the number of apples that Adam eats in one week.

b

If Adam buys 44 apples, how many days will this last him?

6

Dave can wash 2 cars in 4 minutes.

a

How long would it take for him to wash 1 car?

b

How long would it take him to wash 20 cars?

7

Eileen can wash 7 plates in 28 minutes and lace 11 boots in 55 minutes.

a

How long does it take to wash 1 plate?

b

How long does it take to lace 1 boot?

c

How long would it take for Eileen to wash 13 plates and lace 19 boots?

8

In a library, there are 400 books per shelf. How many books are there in a row of 7 shelves?

9

The amount of pears that can fit in a plastic bag is 11 pears per bag. How many bags will be needed to carry 33 pears?

10

There are 224 tissues per box. If the manufacturer wastes 1120 tissues in production, how many boxes of tissues are wasted?

11

The height of a pool increases by 0.5 \text{ cm} for every 10 \text{ L} of water added. After adding some water, the height of the pool increased by 0.45 \text{ m}. How much water was added to the pool?

12

Iain earns \$22 per hour working as a performer. If Iain works for 20 hours a week, determine his weekly earnings.

13

Caitlin plays cricket over the summer holidays. Caitlin scores at rate of 24 runs per game and there are 30 games in the season. Calculate the total runs that Caitlin scored in the season.

14

The volume of polyethylene used to create 81 plastic bags is approximately 18 \text{ mL}. How much polyethylene would be required to create 9 plastic bags?

15

An industrial detergent requires 19 \text{ mL} of water to be added to every 1 \text{ mL} of the detergent for safe usage. How many litres of water must be added to 610 \text{ mL} of detergent?

16

In 2017, the literacy rate in Cuba was 98 people for every 100 in the population, while in Chad, it was 35 people for every 100 in the population. This is the rate of the population aged 15 and above who can, with understanding, read and write a short, simple statement on their everyday life.

How many literate people would you expect:

a
For a town in Cuba with a population of 83\,000?
b
For a town in Chad with a population of 478?
17

In 2019, the population growth of Papua New Guinea was 22 per 1000 while in Oman, the population growth was 91 per 1000. This means that for every 1000 people, the number of people at the end of the year would be 1022 in Papua New Guinea and 1091 in Oman.

Calculate the population at the end of the year for the following towns, rounded to the nearest integer.

a
A town in Papua New Guinea with a population of 19\,000.
b
A town in Oman with a population of 810.
Heart rates
18

Tina counts 26 heart beats over a 20 second interval.

a

How many lots of 20 seconds are in 1 minute?

b

Calculate Tina's heart rate in beats per minute (\text{bpm}).

19

Valerie counts 12 heart beats over a 10 second interval. What is her heart rate in beats per minute (\text{bpm})?

20

Calculate the heart rate in beats per minute for the following recorded pulses:

a
A pulse was recorded beating at 38 times per 30 seconds.
b
A pulse was recorded beating at 17 times per 15 seconds.
c
A pulse was recorded beating at 11 times per 10 seconds.
21

Michael is attending to a patient on the way to the emergency department. In the ambulance, he takes a quick measurement of the patient's heart rate, and finds it to be 30 beats over 15 seconds. An hour later, in the hospital he takes a more detailed measurement and finds the patient's heart rate to be 189 beats over 90 seconds.

a

Calculate the heart rate of the first recording.

b

Calculate the heart rate of the second recording.

c

State whether the patient's heart rate increased or decreased.

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Outcomes

1.1.17

convert units of rates occurring in practical situations to solve problems. For example, 1 tablespoon (tbsp) = 4 teaspoons (tsp) or 1 tbsp = 20 ml (Australia) or 15 ml (US and UK)

1.1.18

use rates to make comparisons

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