### Video Transcript

The grid shows five numbers. 22, 23, 24, 25, 26. From the numbers in the grid, part
one: state the prime number. Part two: state the square
number.

Right, to answer part one of this
question, we need to remember the definition of a prime number. A prime number is a number which
has exactly two factors. Now, you may have had the
definition that a prime number is a number which can only be divided by one and
itself. But there’s a problem with this
definition, if we consider the number one.

Now, one fits the second
description of a prime number because it can be divided by one and also it can be
divided by itself, as itself is one. However, one is not a prime
number. So if instead, we use this first
definition, that a prime number is a number which has exactly two factors, we can
see that one is not a prime number as it does not have two distinct factors. So we’ll use the definition of a
prime number as a number which has exactly two factors rather than a number which
can be divided by one and itself.

To find the prime number in the
list, we need to look for the number then which only has two factors. Each number will have themselves
and one as two factors. So we’re looking to see whether
they have any others. We can eliminate all of the even
numbers straightaway, as they can all be divided by two. Now two, in fact, is the only even
prime number. All other even numbers are not
prime. So we’re left with just 23 and
25.

Now 25, you’ll probably recognize
from your five times table. It’s equal to five multiplied by
five. Which means 25 is not a prime
number as it has three factors: one, five, and 25. 23 is the only number left and it
is indeed a prime number. You could check this by seeing if
you can divide it by numbers like three. And you’ll always find that there
is a remainder. In any case, it’s a good idea to
try and be familiar with prime numbers up to about 30 so that you can recognize them
easily.

Now, let’s consider part two of the
question where we’re asked to state which number is a square number. A square number is the result of
multiplying a positive integer or whole number by itself, which is called squaring a
number. For example, nine is a square
number because it’s equal to three multiplied by three. We can list out some square numbers
to help us answer this question.

One multiplied by one is one. Two multiplied by two is four. Three multiplied by three is nine,
as we’ve already said. Four multiplied by four is 16. And five multiplied by five, which
we also saw in part one of this question, is 25. 25 is the only one of these numbers
that appears in the grid. So 25 is the square number. It’s also a good idea to memorize
square numbers up to about 12 squares, as you could be asked about square numbers in
lots of different contexts.