Transum Software

How Many Triangles?

A self marking step by step approach to calculating the number of triangles in a design.

How Many Triangles? How Many Squares? How Many Rectangles? Information More Puzzles

The first few questions are about counting the number of triangles in this design:

How Many Triangles?

1. Let's start by counting the number of small triangles; the triangles that do not have any lines going through them like this blue one:

One piece triangle

Correct Wrong

2. Next count the number of triangles made from two pieces. The green triangle shown here is one example:

Two piece triangle

Correct Wrong

3. Now count the number of triangles made from three pieces like this red one:

Three piece triangle

Correct Wrong

4. Count the number of triangles made from four pieces like this yellow one:

Four piece triangle

Correct Wrong

5. Count the number of triangles made from six pieces like this purple one:

Six piece triangle

Correct Wrong

6. Add up your answers above to calculate the total number of triangles in this design.

Six piece triangle

Correct Wrong

7. How many one piece triangles are in this design?

One piece triangle

Correct Wrong

8. How many four piece triangles are in this design?

Six piece triangle

Correct Wrong

9. How many triangles are there altogether in this design?

Triangle Design

Correct Wrong

10. How many triangles are there altogether in this design?

Square Design

Correct Wrong


Try your best to answer the questions above. Type your answers into the boxes provided leaving no spaces. As you work through the exercise regularly click the "check" button. If you have any wrong answers, do your best to do corrections but if there is anything you don't understand, please ask your teacher for help.

When you have got all of the questions correct you may want to print out this page and paste it into your exercise book. If you keep your work in an ePortfolio you could take a screen shot of your answers and paste that into your Maths file.

Why am I learning this?

Mathematicians are not the people who find Maths easy; they are the people who enjoy how mystifying, puzzling and hard it is. Are you a mathematician?

Comment recorded on the s /Indice 'Starter of the Day' page by Busolla, Australia:

"Thank you very much for providing these resources for free for teachers and students. It has been engaging for the students - all trying to reach their highest level and competing with their peers while also learning. Thank you very much!"

Comment recorded on the 28 May 'Starter of the Day' page by L Smith, Colwyn Bay:

"An absolutely brilliant resource. Only recently been discovered but is used daily with all my classes. It is particularly useful when things can be saved for further use. Thank you!"

Each month a newsletter is published containing details of the new additions to the Transum website and a new puzzle of the month.

The newsletter is then duplicated as a podcast which is available on the major delivery networks. You can listen to the podcast while you are commuting, exercising or relaxing.

Transum breaking news is available on Twitter @Transum and if that's not enough there is also a Transum Facebook page.

Featured Activity

Polygon Pieces

Polygon Pieces

Arrange the nine pieces of the puzzle on the grid to make the given polygon. Level one is for those learning the names of shapes while other levels are for those who like a challenge!


There are answers to this exercise but they are available in this space to teachers, tutors and parents who have logged in to their Transum subscription on this computer.

A Transum subscription unlocks the answers to the online exercises, quizzes and puzzles. It also provides the teacher with access to quality external links on each of the Transum Topic pages and the facility to add to the collection themselves.

Subscribers can manage class lists, lesson plans and assessment data in the Class Admin application and have access to reports of the Transum Trophies earned by class members.

If you would like to enjoy ad-free access to the thousands of Transum resources, receive our monthly newsletter, unlock the printable worksheets and see our Maths Lesson Finishers then sign up for a subscription now:


Go Maths

Learning and understanding Mathematics, at every level, requires learner engagement. Mathematics is not a spectator sport. Sometimes traditional teaching fails to actively involve students. One way to address the problem is through the use of interactive activities and this web site provides many of those. The Go Maths page is an alphabetical list of free activities designed for students in Secondary/High school.

Maths Map

Are you looking for something specific? An exercise to supplement the topic you are studying at school at the moment perhaps. Navigate using our Maths Map to find exercises, puzzles and Maths lesson starters grouped by topic.


If you found this activity useful don't forget to record it in your scheme of work or learning management system. The short URL, ready to be copied and pasted, is as follows:

Alternatively, if you use Google Classroom, all you have to do is click on the green icon below in order to add this activity to one of your classes.

It may be worth remembering that if should go offline for whatever reason, there is a mirror site at that contains most of the resources that are available here on

When planning to use technology in your lesson always have a plan B!


Friday, January 23, 2015

"This activity is all about breaking down a big difficult task into smaller, more achievable tasks. Not everyone can come up with an effective strategy for themselves so a structured guide like this exercise is a way of helping them learn. There are many other activities related to the process of counting strategies on the Combinations and Permutations section of this website."

Guillaume, France

Sunday, September 18, 2016

"Hi !
On the page "How many triangles", at question #2:
"Next count the number of triangles made from two pieces like this green one:" Your expected answer is 12 but I can only find 6 of them... Is there an error?
Best regards.

[Transum: Thank you Guillaume for your comment. The other green triangles are equilateral triangles so are not similar in shape to the example given. On reflection the wording of the question possibly suggested that it was shapes similar to the example that you should count and indeed there are only six of them. I have changed the wording of the question to make it more clear that it is all two-piece triangles that should be counted.]"

Do you have any comments? It is always useful to receive feedback and helps make this free resource even more useful for those learning Mathematics anywhere in the world. Click here to enter your comments.


©1997-2024 WWW.TRANSUM.ORG

© Transum Mathematics 1997-2024
Scan the QR code below to visit the online version of this activity.

This is a QR Code




This self marking quiz takes you through the stages of a systematic approach to solving the 'How Many Triangles?' question.

How Many Triangles?

You might find it helpful to print out this page containing a number of copies of the designs so that you can colour in the triangles you find.

More Puzzles including lesson Starters, visual aids and investigations.

Answers to this exercise are available lower down this page when you are logged in to your Transum account. If you don’t yet have a Transum subscription one can be very quickly set up if you are a teacher, tutor or parent.

Log in Sign up

Curriculum Reference

See the National Curriculum page for links to related online activities and resources.