Math Calculations & Conversions : Canceling Fractions

Hi, I’m Steve Jones and I’m going to talk
about canceling fractions. Well, we know what a fraction looks like. Twenty-one over twenty-seven
is a fraction; twenty-four over thirty is a fraction. I’m using numbers like this because
they’re slightly more difficult. If I want to cancel two fractions, what I’ve got to
do is inspect them first and see if there’s anything obvious about how I can cancel them
down. Canceling means looking for the same number in the top and the bottom and then
dividing top and bottom by that number. But if you look at the top and bottom here. Well
two plus one is three, and three divides by three. Two plus seven is nine; nine divides
by three. It mean both of these numbers divides by three. So if I divide this one by three–twenty-one
divided by three–gives me seven. Now twenty-seven divided by three, therefore gives me nine.
So in fact, I’ve canceled the fraction and the fraction is seven-ninths. I can do the
same with this fraction, twenty-four over thirty. And the reason I’ve selected this
is because we’re looking for simplifications all the time, and it’s very obvious–two even
numbers–they must divide by two. So twenty-four will not be twenty-four– divided by two–it
will be twelve. And if I divide thirty by two, as well, I’m going to get fifteen. But
with twelve divided by fifteen, I know I haven’t finished, because looking at them, both of
those I know divide by three. Twelve divided by three is four, and fifteen divided by three
is five. So my result is four-fifths. What I’m trying to do when I’m canceling fractions
is to get the simplest number, so that I can’t go any further. I can’t divide top and bottom
by the same number. Just keep it simple.

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