We have had some partial solutions sent in for this quite difficult problem. Well done to Students from the Mef School in Turkey for their attempts. Cansu, Eylül and Kutay realised that if you choose the three numbers 18, 4 and 9, you can solve part of the problem.

18+4-9=13 and if the answer is reversed this number you get is 31.

But is this half the 'product' of the three numbers chosen? If all of the conditions are not met then you haven't arrived at the solution.

The pupils realise that if at first you don't succeed then... you don't give up but you have say to yourself, "keep changing the numbers around until I finally get the answer I have been waiting for." Great advice from Cansu, Eylül and Kutay .

Good number hunting!

We now have a complete solution of this problem from Vivian, Tran, Calise and Chanel from St Felix Primary School, Bankstown, NSW, Australia. They suggest that the numbers are 1, 6, and 7. 6+7=13. Take away 1 and the answer is 12.

The product of 1, 6 and 7 is 42. Half of 42 is 21. Reverse the digits and you get 12. Very tricky!

Well done Vivian, Tran, Calise and Chanel!