Ratio, maps, scales and best value
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 7 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Mixing paint
- What a ratio says
Read the transcript of the teaching part
Last time
Before we start: last time, in Unit conversion, rates and speed, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Mixing paint
To make a green you mix three parts blue with two parts yellow. Double the amounts and the colour stays the same. That is what a ratio is. Today you simplify ratios, share amounts in a ratio, read map scales, and decide which pack is the best value.
What a ratio says
A ratio compares quantities in the same units. Three to two means three parts of one thing for every two parts of another. To simplify, divide every number by the highest common factor. Thirty-six to forty-eight: both divide by twelve. If the units differ, change them first. Forty grams to two kilograms is forty to two thousand. To write it as one to n, divide by the first number. Forty goes into two thousand fifty times, so it is one to fifty.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Sharing in a ratio.
The whole chapter: Ratio, Proportion and Rates.
Chapter 6: Ratio, rate and proportion
- Ratio, maps, scales and best value 5 min
- Rates, unit conversion and speed 6 min
Also for IGCSE Maths 0580
Which topics come up most in IGCSE Maths 0580 past papers, counted from every paper since 2004.