Online Psychic

A Maths Starter of The Day

I can read your mind!

PsychicThink of a two digit number,*

Reverse the digits to get another two digit number,

Subtract the smaller two digit number from the other,

Add the digits of your answer together

I know what your answer is!

 

(* The two digits must be different)

9

How did I know?

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Keywords: Starter | Algebra | Place Value | Puzzles

  • Tom, Birmingham
  • Sunday, January 13, 2008
  • "75-57?

    I think the answer will be a multiple of 9?"
  • Paul, Coventry
  • Tuesday, January 15, 2008
  • "Yes, and when you add the digits of a two digit multiple of 9 the answer is always 9"
  • JM, Ysgol Friars
  • Monday, January 19, 2009
  • "AB - BA = (Ax10+B)-(Bx10+A) = 9A-9B = 9(A-B)"
  • CF, Lancshire
  • Thursday, January 21, 2010
  • "This is a great starter it is a quick way to see who can subtract without a calculator and it is a good way to demonstrate the use of algebra to generalise and prove things."

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This starter has scored a mean of 4.1 out of 5 based on 80 votes.

 

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