1. Using fractions and percentages
[N3.1 Core Plenary]
1) Which is the better offer: “One third off” or “30% off? Use some examples to support your answer.
2) Amy has some red, blue, green and black counters.
50% are red, 30% blue, 15% green and 5% black. What is the least number of counters she could have?
3) A computer manufacturer has 50% of the market. This year this increased by 10%. What was its percentage share of the market in this year?
Why are there two possible answers you could give?
30% off!!
Preamble
These three questions provide practice in applying children’s knowledge of fractions and percentages. The initial question may seem very obvious but misunderstanding between “off” and “of” and a third and 30% are surprisingly common. Some pupils may need some initial support, therefore working in groups may be useful, especially for the “least number” part in (2). Question (3) is a very common ambiguity and can produce some rewarding discussion, and it does arise in the media.
Possible content
Using fractions and percentages.
Resources
None.
Solution/Notes
1) One third is the better deal (1/3 is greater than 30/100)
2) 10 blue, 6 red, 3 green and 1 black. Pupils could start with 50, 30, 15, and 5, then divide throughout by 5.
3) Either of these are correct : 55% (increase of 10% on 50%) or 60% (50%+10%) (Here might be an suitable point to discuss 100% increases and the impossibility of 100% deceases etc.)
Original Material © Cambridge University Press 2010
Original Material © Cambridge University Press 2010