Video Transcript
There were 15 birds on a tree, but
a third of them flew away. Find the number of birds that flew
away.
To begin with in this problem,
we’re told about a group of birds. There were 15 of them on a
tree. Let’s model our 15 birds using
plastic counters. Now, we’re told that some of these
birds flew away. And fortunately, we’re not told the
number of birds that flew away. This is what we need to find. Instead, we’re told the fraction of
the whole amount. This is a third. Now this is a third written in
words. But do you remember how to write it
using digits? The numerator is one. This shows us that we’re only
thinking about one-third and not two-thirds or more. And then the denominator is
three. This shows us the number of equal
parts that we need to split the whole into.
So to find one-third of 15, we can
divide 15 by the denominator, three. If we split 15 into three equal
groups, how many will there be in each group? Perhaps you can think of a times
tables fact that could help us here. We know that three times five
equals 15. 15 divided by three equals
five. And we can show this using our
counters. We’ve split the whole amount into
three equal groups, and each of the three groups, that’s each third, is worth
five. So if there were 15 birds on a
tree, but a third of them flew away, the number of bird that flew away is five.
