School exams have just taken place - delayed due to a bout of illness at the end of last term. In my year 5 exam, as a filler for those who finished early, I set the question:
Using the digits 1, 2, 3, 4, 5, 6, 7, 8, and 9 in order and the signs + and -, can you make 10?
To be fair to them, they had a good go, but no one managed to get the answer. It was only when we went through it that I realised it is superficially an impossible question. Using odds and evens, can you see why?
It is only when you combine two digits into one value that it is possible to make 10. One possible solution is:
12 + 3 - 4 - 5 - 6 - 7 + 8 + 9
"But why would you ask us a question that had no answer?" was the cry...
I smiled smugly in response!
This is a variation on a similar problem to make 100 using all digits in order.
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