Question - St. Pauls sample paper 1

[enema]

Does anyone know the answer to St. Paul's maths paper sample 1, paper b, Q10:

4 of the 5 jigsaw pieces shown below fit together to make a square - which does not fit?

(Downloadable http://spgs.org/wp-content/uploads/2014 ... aper-1.pdf) page 15

We thought B as the square must equal 5 sides in length, and the total number of squares in shapes A, C, D and E would equal 25. But obviously am not sure, hence asking.

Many thanks

[Guest55]

I think that is the only way to get a square number by adding four of the following numbers (squares in each piece):

A: 4 B: 5 C: 6 D: 7 E: 8

[enema]

Thought so, thanks for confirming Guest55.

[Proud_Dad]

Yes like you both said each piece has a different number of squares and if you add them all up it totals 30 small squares. The completed puzzle must contain between 22 and 26 squares depending on which piece you don't use so if its a square it has to be 25 small squares (5 x 5) so the answer must be B.

Quite a clever question this. A lot of people's first instinct might be to try and work out how different combinations of pieces fit together to make a square, which would be very tricky to do in your head, but a bit of lateral thinking and knowledge of square numbers gives the answer.