Interview riddle

On the Mathematics chat we were recently talking about the following problem @Chris’ssis had to solve during an interview :

3\times 4=8
4\times 5=50
5\times 6=30
6\times 7=49
7\times 8=?

We have not managed to solve it so far, all we know is the solution (which was given after we had given up) :


How do we find this solution ?


These interview problems are sometimes weird, where notations are bad, rules are arbitrary, and they expect only one answer where several could fit.

Here is one, which could be the expected one, but probably not:

To compute a \times b, take the numerator of \dfrac{ab^2}{6} after simplification of the fraction.

I don’t see how they could argue it is wrong.

Source : Link , Question Author : Hippalectryon , Answer Author : Denis

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