Challenge 3 - Rectangles
Challenge 3 is all about rectangles.
Maths teacher Chris Smith and pupils from Grange Academy are here to explain.
The Maths Week Scotland Daily Challenges have been set by the Scottish Mathematical Council.
Mr Smith: This problem is all about rectangles.
This design is made of dominoes (rectangles measuring 1 × 2).
How many rectangles (of all sizes) does the design contain?
Explain your answer.
Pupil: Think about all the different sizes of rectangles
Pupil: Remember that rectangles can overlap each other.
Pupil: And remember that any shape with four sides and four right angles is a rectangle.
Pupil: Good luck!
So here's the challenge:
This problem is all about rectangles.
This design is made of dominoes (1 × 2 rectangles).
How many rectangles (of all sizes) does the design contain?

Need a hint?
Think about all the different sizes of rectangles
Remember that rectangles can overlap each other.
Remember that any shape with four sides and four right angles is a rectangle.
Solution
Worked out the answer? Here's how you can do it.
Did you work out the number of rectangles in this design?
Let’s look at how we got our answer.
The individual dominoes of 1 × 2 are rectangles. There are 12 of them.
There are also:
Six 2 × 3 rectangles…
Two 2 × 4 rectangles…
Two 3 × 4 rectangles…
Two 2 × 5 rectangles…
Two 2 × 6 rectangles…
And one 4 × 6 rectangle (i.e. the whole figure).
There are also four 2 × 2 squares.
Squares have four sides and four right angles, so they are also rectangles.
So, there are 12 + 6 + 2 + 2 + 2 + 2 + 1 + 4 = 31 rectangles in the design.
Great job if you pieced this one together.
Step 1
Look at all the different possible sizes of rectangle that can be made. Count up the number of rectangles of each size:
- twelve1 × 2 rectangles
- six2 × 3 rectangles
- two2 × 4 rectangles
- two2 × 5 rectangles
- two2 × 6 rectangles
- two 3 × 4 rectangles
Don't forget, there's also the whole rectangle of the design: one4 × 6 rectangle.
There are also four2 × 2 squares. Squares have four sides and four right angles, so they also count as rectangles.
Click through the slideshow to see all the possible sizes of rectangle

Image caption, There are twelve 1 × 2 rectangles

Image caption, There are six 2 × 3 rectangles

Image caption, There are two 3 × 4 rectangles

Image caption, There are two 2 × 4 rectangles

Image caption, There are two 2 × 5 rectangles

Image caption, There are two 2 × 6 rectangles

Image caption, There is one 4 × 6 rectangle. This is the whole shape made up of all the dominoes.

Image caption, There are also four, 2 × 2 squares. A square has four sides and four right angles, so it counts as a particular type of rectangle.
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Step 2
Now we can add the total number of each size of rectangle together:
12 + 6 + 2 + 2 + 2 + 2 + 1 + 4 = 31
There are 31 rectangles in total in the design.

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