YEAR 8 MATHS FOCUS
NUMBER AND ALGEBRA
Percentages
Learning Experiences
Concept Teaching
Percentages
PERCENTAGES
OUTCOME
A student:
MA4-5NA:
operates with fractions, decimals and percentages
| TEACHING POINTS | One-cent and two-cent coins were withdrawn by the Australian Government in 1990. When an amount of money is calculated, it may have 1, 2, 3 or more decimal places, e.g. when buying petrol or making interest payments. When paying electronically, the final amount is paid correct to the nearest cent. When paying with cash, the final amount is rounded correct to the nearest five cents, eg $25.36, $25.37 round to $25.35 |
| LANGUAGE | In questions that require calculating a fraction or percentage of a quantity, some students may benefit from first writing an expression using the word ‘of’, before replacing it with the multiplication sign (×). Students may need assistance with the subtleties of the English language when solving word problems. The different processes required by the words ‘to’ and ‘by’ in questions such as ‘find the percentage increase if $2 is increased to $3’ and ‘find the percentage increase if $2 is increased by $3’ should be made explicit. When solving word problems, students should be encouraged to write a few key words on the left-hand side of the equals sign to identify what is being found in each step of their working. The word ‘cent’ is derived from the Latin word centum, meaning ‘one hundred’. ‘Percent’ means ‘out of one hundred’ or ‘hundredths’. |
| PURPOSE RELEVANCE OF SUBSTRAND | ‘Decimals’ and ‘percentages’ represent different ways of expressing fractions (and whole numbers), and so are other ways of representing a part of a whole. Fractions (and decimals and percentages) are of fundamental importance in calculation, allowing us to calculate with parts of wholes and to express answers that are not whole numbers, e.g. 4÷5=45 (or 0.8 or 80%). |
Expectations of Attainment
Compare fractions using equivalence; locate and represent positive and negative fractions and mixed numerals on a number line (ACMNA152) | determine the highest common factor (HCF) of numbers and the lowest common multiple (LCM) of numbers |
| generate equivalent fractions | |
| write a fraction in its simplest form | |
| express improper fractions as mixed numerals and vice versa | |
| place positive and negative fractions, mixed numerals and decimals on a number line to compare their relative values | |
| – interpret a given scale to determine fractional values represented on a number line {Problem Solving} | |
| – choose an appropriate scale to display given fractional values on a number line, e.g. when plotting thirds or sixths, a scale of 3 cm for every whole is easier to use than a scale of 1 cm for every whole {Communicating, Reasoning} |
Solve problems involving addition and subtraction of fractions, including those with unrelated denominators (ACMNA153) | add and subtract fractions, including mixed numerals and fractions with unrelated denominators, using written and calculator methods |
| – recognise and explain incorrect operations with fractions, e.g. explain why 2/3+1/4≠3/7 {Communicating, Reasoning, Literacy, Critical and creative thinking} | |
| – interpret fractions and mixed numerals on a calculator display {Communicating, Critical and creative thinking} | |
| subtract a fraction from a whole number using mental, written and calculator methods, e.g. 3−2/3=2+1−2/3=2 1/3 |
Multiply and divide fractions and decimals using efficient written strategies and digital technologies (ACMNA154) | determine the effect of multiplying or dividing by a number with magnitude less than one |
| multiply and divide decimals by powers of 10 | |
| multiply and divide decimals using written methods, limiting operators to two digits | |
| – compare initial estimates with answers obtained by written methods and check by using a calculator {Problem Solving, Critical and creative thinking} | |
| multiply and divide fractions and mixed numerals using written methods | |
| – demonstrate multiplication of a fraction by another fraction using a diagram to illustrate the process {Communicating, Reasoning, Literacy} | |
| – explain, using a numerical example, why division by a fraction is equivalent to multiplication by its reciprocal {Communicating, Reasoning, Literacy, Critical and creative thinking} | |
| multiply and divide fractions and decimals using a calculator | |
| calculate fractions and decimals of quantities using mental, written and calculator methods | |
| – choose the appropriate equivalent form for mental computation, e.g. 0.25 of $60 is equivalent to 1/4 of $60, which is equivalent to $60 ÷ 4 {Communicating, Critical and creative thinking} |
Express one quantity as a fraction of another, with and without the use of digital technologies (ACMNA155) | express one quantity as a fraction of another |
| – choose appropriate units to compare two quantities as a fraction, e.g. 15 minutes is 15/60=1/4 of an hour {Communicating, Critical and creative thinking} |
Round decimals to a specified number of decimal places (ACMNA156) | round decimals to a given number of decimal places |
| use symbols for approximation, e.g. ≑ or ≈ {Literacy} |
Investigate terminating and recurring decimals(ACMNA184) | use the notation for recurring (repeating) decimals, e.g. 0.33333…=0.3˙, 0.345345345…=0.3˙45˙, 0.266666…=0.26˙ {Literacy} |
| convert fractions to terminating or recurring decimals as appropriate | |
| – recognise that calculators may show approximations to recurring decimals, and explain why, e.g. 23 displayed as 0.666666667 {Communicating, Reasoning, Critical and creative thinking} |
Connect fractions, decimals and percentages and carry out simple conversions (ACMNA157) | classify fractions, terminating decimals, recurring decimals and percentages as ‘rational’ numbers, as they can be written in the form ab where a and b are integers and b≠0 {Literacy} |
| convert fractions to decimals (terminating and recurring) and percentages | |
| convert terminating decimals to fractions and percentages | |
| convert percentages to fractions and decimals (terminating and recurring) | |
| – evaluate the reasonableness of statements in the media that quote fractions, decimals or percentages, e.g. ‘The number of children in the average family is 2.3’ {Communicating, Problem Solving, Critical and creative thinking} | |
| order fractions, decimals and percentages |
Investigate the concept of irrational numbers, including π (pie) (ACMNA186) | investigate ‘irrational’ numbers, such as π and √2 {Literacy Critical and creative thinking} |
| – describe, informally, the properties of irrational numbers {Communicating, Literacy} |
Find percentages of quantities and express one quantity as a percentage of another, with and without the use of digital technologies (ACMNA158) | calculate percentages of quantities using mental, written and calculator methods |
| choose an appropriate equivalent form for mental computation of percentages of quantities, e.g. 20% of $40 is equivalent to 1/5 × $40, which is equivalent to $40 ÷ 5 {Communicating, Critical and creative thinking} | |
| express one quantity as a percentage of another, using mental, written and calculator methods, e.g. 45 minutes is 75% of an hour |
Solve problems involving the use of percentages, including percentage increases and decreases, with and without the use of digital technologies (ACMNA187) | increase and decrease a quantity by a given percentage, using mental, written and calculator methods |
| – recognise equivalences when calculating percentage increases and decreases, e.g. multiplication by 1.05 will increase a number or quantity by 5%, multiplication by 0.87 will decrease a number or quantity by 13% {Reasoning} | |
| interpret and calculate percentages greater than 100, e.g. an increase from $2 to $5 is an increase of 150% | |
| solve a variety of real-life problems involving percentages, including percentage composition problems and problems involving money | |
| – interpret calculator displays in formulating solutions to problems involving percentages by appropriately rounding decimals {Communicating, Information and communication technology capability} | |
| – use the unitary method to solve problems involving percentages, e.g. find the original value, given the value after an increase of 20% {Problem Solving} | |
| – interpret and use nutritional information panels on product packaging where percentages are involved {Problem Solving, Literacy} | |
| – interpret and use media and sport reports involving percentages {Problem Solving, Critical and creative thinking} | |
| – interpret and use statements about the environment involving percentages, e.g. energy use for different purposes, such as lighting {Problem Solving, Critical and creative thinking, Sustainability} |
Learning Experiences
to be added
Concept Teaching
links to be added