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# Pre-algebra

Community Questions
Ratios, proportions, units, and rates
All content in “Ratios, proportions, units, and rates”

### Ratios and proportions

Would you rather go to a college with a high teacher-to-student ratio or a low one? What about the ratio of girls-to-boys? What is the ratio of eggs to butter in your favorite dessert? Ratios show up EVERYWHERE in life. This tutorial introduces you to what they (and proportions) are and how to make good use of them!

### Rates

How fast can a robot possum fly? What is the rate at which a hungry you can consume avocados? This tutorial helps you make sense of these fundamental questions in life.

### Unit conversion

Wait, I'm in Europe and my car only tells my distance traveled in kilometers! But I'm used to a units of distance devised by the Romans to measure the average length of 1000 paces of a soldier (the "mile")! How do I operate? This tutorial is about the fundamental skill of unit conversion. Sal's cousin Nadia being a bit confused with this was actually the reason why he started tutoring her (which led to the creation of the Khan Academy).

### Metric system unit conversion

You might be surprised to realize that only two countries in the world use feet, miles, or yards or a bunch of other "English System" conventions (the irony being that the English don't even use the "English System" any more). Everyone else, including the English, now use the metric system which is actually much more logical. Learn about kilo and milli and centi and become a metric unit megastar!

### Fahrenheit and Celsius conversion

There are three major conventions for measuring temperature in the world, Fahrenheit, Celsius and Kelvin. If converting between the three gives you cold feet, then this tutorial might warm them up.