### Video Transcript

A cylinder-shaped jar of jam has a
circular base of radius seven. Use twenty two over seven as an
approximation of đťś‹ to calculate the perimeter of the base.

Okay, letâ€™s draw a quick sketch of
our jar of jam. Itâ€™s a cylinder shape, so there it
is. And weâ€™re told that it has a
circular base of radius seven units. Weâ€™re not told what those units are
so we wonâ€™t be able to write those down, but seven units. So the radius is the distance from
the centre of a circle to its circumference.

Now weâ€™re trying to work out the
length of the perimeter of the base. Weâ€™re told the base is a circle so
we want to know the perimeter of a circle radius seven. Now weâ€™ve got two possible formulae
that we could work with. We could do đťś‹ times the diameter
of the circle or we could do two times đťś‹ times the radius of the circle. Now weâ€™ve been given the radius in
this case, so weâ€™re gonna use the second of those formulae.

So thatâ€™s two times, and then we
were told to use twenty-two over seven as an approximation of đťś‹, so weâ€™re gonna
write two times twenty-two over seven. And we were told that the radius
was seven.

So our calculation becomes two
times twenty-two over seven times seven. Now Iâ€™m gonna turn this into a
proper fraction calculation. But instead of writing two, Iâ€™m
gonna write two over one. And instead of writing seven, Iâ€™m
gonna write seven over one. And now when weâ€™re multiplying
fractions together, I can just multiply all the tops together and then all the
bottoms together, all the numerators together and then all the denominators
together. But before I do that, I can see
that Iâ€™ve got a seven as one of the numerators but Iâ€™ve also got a seven as one of
the denominators, so I can do some cancelling. If I do seven divided by seven, I
get one. If I do seven divided by seven, I
also get one. So Iâ€™ve got two over one times
twenty-two over one times one over one.

Well two times twenty-two times one
is forty-four, and one times one times one is one. Well forty-four over one is just
the same as forty-four. And we werenâ€™t told specifically
what the units were, so Iâ€™m just gonna write forty-four units. So there we have our answer:
forty-four units.