Some friends came to visit last weekend, and we got to talk about the following problem, which seems to have made the news headlines (it was given at a math contest for ten year olds and apparently many math teachers couldn't figure out a solution):

We have numbers 1, 3, 4 and 6. Create an expression using any elementary operators (+, -, *, /), containing only these numbers, exactly once each, such that the result is 24.

(if you'd like to try finding a solution, stop reading now because there's a spoiler here)

I felt the problem itself is inappropriate for 10 y.o. kids and irrelevant for a maths contest; but it seemed like a good programming exercise, so I told'em “while you're banging your heads to guess a solution, I'll go and write a program to give me all solutions.”

I implemented it in Scheme, because it requires backtracking and using continuations for this is a joy. But in this blog post I'll work out the solution in JavaScript.

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