### Video Transcript

Which of the following is closest
to the weight of a tennis ball? 20 kilograms, 25 kilograms,
one-quarter kilogram, 50 kilograms, or 30 kilograms.

In this question, we need to
estimate the weight or the mass of a tennis ball. We know we need to estimate to find
the answer because the question asks us to find the measurement that is closest to
the weight of a tennis ball. It doesn’t ask us the actual
amount, but the amount that is nearest. So we need to use our knowledge of
measurements in real life to estimate the amount.

The first thing we can say about
our five possible answers is that they’re all written in the same unit of
measurement. They’re all a number of
kilograms. This makes it easier to compare
them if we need to. The second thing that we can notice
about our possible answers is that four of them are above one whole kilogram. In fact, there are a lot more than
one whole kilogram. They’re all 20 kilograms or
more. There’s only one measurement that
is less than a kilogram, and that’s one-quarter kilogram.

Now, to estimate the answer, we
need to use our knowledge of the real world. First of all, what do we know about
tennis balls? Well, amongst the other things,
they’re made of rubber, which makes them easy to bounce and to hit. They’re filled with air, which, of
course, makes them light enough to throw in the air and to hit and so on. We know that the whole aim of the
game involves hitting the ball over the net and pass to your opponent. So the ball has to be fairly light
for us to be able to do that.

The other real-world fact that we
can think about to help us estimate the answer is to understand what one kilogram is
worth. Sugar is often sold in bags of one
kilogram. So it’s useful to visualize a bag
of sugar when we’re thinking about how heavier kilogram is. We can see now how a lot of our
answers are really silly. 20 kilograms is the same as 20 bags
of sugar. Imagine hitting a tennis ball that
weigh the same as 20 bags of sugar. In the same way, 25 kilograms, 30
kilograms, and even 50 kilograms are far too heavy for a tennis ball.

Using everything we know about
tennis balls and kilograms, the best estimate is the one that is less than a whole
kilogram, one-quarter of a kilogram. Out of our five possible answers,
the measurement that is closest to the weight of the mass of a tennis ball is
one-quarter of a kilogram.