[agf]

I think you're referring to this puzzle: http://datagenetics.com/blog/december12014/index.html

The version you gave is missing information and so can't be solved as stated.

[kristjansson]

Thank you for posting this. I read the parent several times trying to figure out if they were mistaken or I was dense.

[CPLX]

I had to read that like 11 times before I started to get the underlying principle. That's amazing.

[hexane360]

In a very similar vein, try this one: https://youtu.be/N5vJSNXPEwA