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Understanding Proportions. Created by Sal Khan and Monterey Institute for Technology and Education.
Video transcript
Is the proportion true or false that 3/12 or 3:12 is equal to 5/35 or 5:35? Now to figure this out, we just have to figure out whether these are equivalent fractions, and the easiest way to do that, is to put both of them in simplified form, and see if we get the same answer. So let's try with 3/12 first. So if we have 3/12, both the numerator and the denominator are divisible by 3. So let's divide by 3. So divide the numerator by 3, and let's divide the denominator by 3. We get 3 divided by 3 is 1. 12 divided by 3 is 4. So 3/12 is the same thing is 1/4. Now let's try do the same thing for 5/35. 5 over 35-- I'm leaving some space so we can divide-- well, these are both divisible by 5, so let's divide the numerator and the denominator by 5. So if we divide the numerator by 5 and the denominator by 5, the numerator, 5 divided by 5 is 1, and then 35 divided by 5 is 7. So this thing is equivalent to saying that 1/4 is equal to 1/7, which is clearly not true. This is clearly not true, so the proportion is false.