Odd one out

Lovely warm-up or “taster “ for L1-2 level groups. The idea could easily be adapted for Entry Level groups.
Just as the quote on the resource says:“The value of the problem is not so much in coming up with the answer as in the ideas and attempted ideas it forces on the would be solver.”
See comments below for some suggested answers. Please add your own answers or suggestions for other suitable groups.

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John didn’t provide an answer sheet: far better to get you and your students thinking and come up with your own.

Here’s some I came up with:

1 – 4 – 25 – 29

  • 4 is the odd one out because it’s the only even number
  • 29 because it’s not a square number
  • 1 because it’s the only prime number

Help! I can’t think of a reason for 25?

5cm – 0.5m – 5 miles – 5l

  • 0.5m is the odd one out because it’s a decimal not a whole number
  • 5 miles because it’s not a metric measure
  • 5l because it’s a measure of capacity not length

I can’t think of a reason for 5cm?

I am sure there are many alternatives.
Please leave a comment if you have further ideas.

1 is less then 2 (1 isn’t a prime)
4 is a multiple of 4
25 is a multiple of 5
29 is a prime, is greater than 28, not a factor of 100

triangle has an odd number of points
square must have all its sides the same length, doesn’t contain the letter g
oblong can’t be regular (can’t have all its sides the same length), only contains 2 vowels
octagon name has an odd number of letters

7/8 – bigger than 1/2, not equivalent to a unit fraction
1/3 – odd denominator
2/8 – can be cancelled, even numerator
1/2 – equals 50%

5cm – cm isn’t a base unit (it is defined as being a part of a metre)

We didn’t look at the graphs.

Mixed L1-L2 group of adults, keen and interested but found it hard to think of any – most I had to think of and steer them towards.

Thank you for your comments. The idea was to probe learners understanding of numbers and come up with ideas that could be debated in the classroom.

John Thompson B