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# Proportion validity example

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.