The diagram shows nine identical squares inside a rectangle. The length of the rectangle is 18cm
Work out the width of the rectangle

18 cm

Step-by-step explanation:

Let X represent a square

For it to be a rectangle, needs to be:

X X X

X X X

X X X

(It's a giant square made of squares)

This works since a square is a rectangle, but a rectangle isn't always a square. No other arrangement of the squares lead to a rectangle.

For Example:

X X X X

X X X X X

It doesn't work because there is an odd number of squares, and only would work if it was a multiple of 3,5,7 etc.. and 3 is the only number that fits.

So if the length is 18cm, the width is also 18cm.

b. astronomers