12, 21, 30, 30, 15, 30, 14, 18, 12, 21, 24, 33, 12, 18, 15, 15, 18, 6, 6, 18, 9, 27, 33, 15, 6, 24, 12, 9, 21, 18, 12, 12, 18, 27, 21, 24, 21, 27, 21, 30, 24, 18, 30, 33, 6, 12, 9, 27, 6, 24.

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
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• 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
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• 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
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• We think this was a very interesting transum.
• Chantel, Newcastle Under Lyme
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• 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,
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• 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
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• 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
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• 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
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• Used as part of Maths week
lots of different answers with great reasons.
• Reece Burgess, Ivybridge
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• The last 27, because is the only one followed by a full stop (Not a comma!).
• Miss Bellis, Northop Hall CP School
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• 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.

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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.

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