Work with Ratios
A ratio can be written 3 different ways:
2 to 3 2 : 3 2 /3
But you read a ratio the same way no matter how it looks.
Say: two to three
A ratio may look like a fraction, but it is really very different.
(You are already familiar with things that look the same but are different. Look at this word: read. What does it say? It depends on the context. It sounds one way in “I can read this sentence.” and another way in “A long time ago, I read a book.” In math, the same sorts of things happen. Symbols can mean different thing in different contexts.)
Fraction: 2/3 Meaning: I had 3 pieces of pizza and my friend ate two of them.
Ratio: 2/3 Meaning: I ate 2 pieces of pizza and my friend ate 3 pieces.
In both cases, there is a comparison. In a fraction, part of something is being compared to the whole thing. In a ratio, two are things are being compared to each other and the whole of anything is irrelevant.
There is a special type of ratio called “per unit.” You’ve already heard about that in real life: ‘kilometres per hour’ when you are in a car, ‘cents per litre’ at a gas station, and ‘dollars per kilogram’ at a grocery store.
‘Per’ means ‘one.’ ‘$1.20 per litre’ means that one litre costs 1 dollar and 85 cents. ‘One hundred kilometres per hour’ means that you can cover 100 km in one hour of travelling. This kind of ratio can be written in 3 different ways: km per hr.; km:hr; km/hr
(Note: the link to the following video and practice sessions will take you away from Ms.RosenReads. While I recommend the sites as I saw them, MsRosenReads cannot be responsible for the continued content or continued availability of other sites. If you encounter a problem, please contact me.)
For a simple lesson, click HERE
This is a 10-minute video. It goes quickly, so use some strategies to help you learn:
– pause frequently and think about what you just heard
– pause and take notes as you are watching
– watch the video several times
When you are ready, practise online:
Equivalent Ratio Word Problems