Odd One Out

110, 80, 50, 30, 110, 110, 20, 50, 80, 90, 50, 110, 40, 110, 40, 30, 100, 60, 90, 110, 70, 50, 50, 70, 30, 60, 110, 30, 100, 30, 30, 80, 70, 100, 29, 20, 90, 30, 50, 110, 60, 20, 30, 100, 90, 60, 80, 70, 100, 90.

Which number is the odd one out? Write down as many reasons as you can think of explaining why that number is the odd one out.

A Mathematics Lesson Starter Of The Day


Topics: Starter | Number

  • Class 1.6, Brechin High School
  • This was a good starter. It would make it more challenging if the odd number appeared more than once, although we did have to justify our answers. The 45, 54 was sneaky!
  • Mr. Melville, Whitehouse Common Primary School
  • Our class 4JM, agreed that 60 would be the odd one out because it isn't in the 8 times table. It also only appears once.
    Good starter for a Year 4 class!
  • Mr. Kavanagh's 5th Class, Cork, Ireland
  • We think this was a very interesting transum.
  • Chantel, Newcastle Under Lyme
  • That was an easy puzzle to do but I rly enjoyed doing it at school and at home. They should do more of these ones.
  • Transum,
  • Note that some of the comments above refer to particular numbers which you may not be able to find. This may puzzle you! Each time this page is loaded the numbers are changed with a different odd one out. This means that you could use this starter a number of times with the same class. A large number of the starters on this site are generated using random numbers. A few hand picked random starters can be found here: Random Starters.
  • Paul Graveling, Norwich
  • My Yr 4 class smashed this one. Rachel said" Our school must be amazing"
    "Keep it up" said Len Boosterman.
  • Year 5, Almondsbury Primary School
  • We found lots of different odd ones out for different reasons. Here are just a few:
    64 because it's not in the 7 times table and it is not repeated.
    77 because it is the only one with 2 digits the same.
    14 because it's the only one less than 20.
    70 because it's the only multiple of 10.
    63 because it's the only one in the 9 times table.
    49 because it's the only odd square number. .
  • Vale Primary School Guernsey, 3B
  • Used as part of Maths week
    lots of different answers with great reasons.
  • Reece Burgess, Ivybridge
  • The last 27, because is the only one followed by a full stop (Not a comma!).
  • Miss Bellis, Northop Hall CP School
  • Year 5 thought 70 becaits is the only multiple of 10 and not repeated.
    Ella said 25 as its is the only one not in the 7 times table and not repeated!
    A great starter to get you thinking!

How did you use this starter? Can you suggest how teachers could present or develop this resource? Do you have any comments? It is always useful to receive feedback and helps make this free resource even more useful for Maths teachers anywhere in the world.
Click here to enter your comments.

If you don't have the time to provide feedback we'd really appreciate it if you could give this page a score! We are constantly improving and adding to these starters so it would be really helpful to know which ones are most useful. Simply click on a button below:

Excellent, I would like to see more like this
Good, achieved the results I required
Didn't really capture the interest of the students
Not for me! I wouldn't use this type of activity.

This starter has scored a mean of 2.9 out of 5 based on 369 votes.

Previous Day | This starter is for 30 April | Next Day



Note to teacher: Doing this activity once with a class helps students develop strategies. It is only when they do this activity a second time that they will have the opportunity to practise those strategies. That is when the learning is consolidated. Click the button above to regenerate another version of this starter with different numbers.

Your access to the majority of the Transum resources continues to be free but you can help support the continued growth of the website by doing your Amazon shopping using the links on this page. Below is an Amazon search box and some items chosen and recommended by Transum Mathematics to get you started.


Have you read Craig's book yet?

Craig Barton must surely be the voice of Mathematics teachers in the UK. His wonderful podcasts interviewing the industry experts have culminated in this wonderful book. As Craig says: "I genuinely believe I have never taught mathematics better, and my students have never learned more. I just wish I had known all of this twelve years ago..." more...

"How I wish I'd taught Maths" is an extraordinary and important book. Part guide to research, part memoir, part survival handbook, it’s a wonderfully accessible guide to the latest research on teaching mathematics, presented in a disarmingly honest and readable way. I know of no other book that presents as much usable research evidence on the dos and don’ts of mathematics teaching in such a clear and practical way. No matter how long you have been doing it, if you teach mathematics—from primary school to university—this book is for you." Dylan Wiliam, Emeritus Professor of Educational Assessment, UCL.

The Craig Barton Book

Casio Classwiz Calculator

There is currently a lot of talk about this new calculator being the best in its price range for use in the Maths classroom. The new ClassWiz features a high-resolution display making it easier to view numerical formulas and symbols but it isn't a graphical calculator as such (it has the capacity to draw graphs on your smart phone or tablet, via a scannable QR code and an app).

As well as basic spreadsheet mode and an equation solving feature you also get the ability to solve quadratic, cubic or quartic polynomial inequalities and the answer is given just as it should be written down, using the correct inequality symbols!

This calculator has a high-performance processor and twice the memory of previous models ensuring speedy operation and superior computational power.more...

Online Maths Shop

Laptops In Lessons

Teacher, do your students have access to computers?
Do they have iPads or Laptops in Lessons?

Whether your students each have a TabletPC, a Surface or a Mac, this activity lends itself to eLearning (Engaged Learning).

Laptops In Lessons

Here a concise URL for a version of this page without the comments.


Here is the URL which will take them to a related student activity.


Student Activity


©1997-2020 WWW.TRANSUM.ORG