### Video Transcript

Which shape is not congruent to the
others?

This problem is a sort of
odd-one-out question. We’re given some shapes and we need
to find the one that’s different. This is because when shapes are
congruent, we know they’re exactly the same size; they’re exactly the same
shape. So, four out of our five shapes are
exactly the same size and shape. But one of them is not
congruent. We’re looking then for the shape
that’s different.

Now, as we’ve just said, there are
two parts, two shapes, being congruent. They must be the same size, and
they must be exactly the same shape. It doesn’t matter what color they
are; it doesn’t matter what position we put them in. But those two factors must be
true. Now, if we look at our five shapes,
we can see that they’re all in different positions. As we’ve just said, this doesn’t
mean they can’t be congruent. We know that two shapes can be
exactly the same, but just in a different position. But it does make them harder to
spot.

One way that we could check which
of these shapes are the same even though they’re in different positions would be to
put a little piece of tracing paper or some sort of paper we can see through over
one of the shapes then trace it and then move it to see if it fits exactly on top of
any of the other shapes. For example, we’ve just proved that
shapes (a) and (d) are congruent.

But you know, perhaps there’s a
quicker way to find the answer here, because not only the shapes need to be exactly
the same shape to be congruent, they need to be exactly the same size. And one of these shapes is not the
same size as any of the others. We don’t need to get a ruler or
anything like that. We can see just by looking with our
eyes that shape (b) is larger than any of the other shapes. So, although we could go from (a)
to (e) and check whether they’re exactly the same shape, perhaps using tracing
paper, we’ve identified what we could call the odd one out because it’s not the same
size as any of the others. The shape that is not congruent is
shape (b).