Silly but trickly puzzle

So my PhD friends couldn’t solve the following problem…

3489 = 4
8410 = 4
9120 = 2
8328 = 4
2210 = 1
9910 = 3
9900 = 4
7172 = 0
3884 = 5
9889 = 6
9009 = 4
0911 = 2
8888 = 8

What is 3859?

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4 Comments.

  1. Hint1: The shape of the numbers.
    Hint2: Think closed loops.
    Hint3: Count the number of closed loops.
    Answer:3

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  2. the shity thing is that there is an infinite number of functions which go through the first 13 ordered pairs so asking what the “next” value is, is kinda dumb.

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  3. I’m not the author of the puzzle. Remember that the title of the puzzle is Silly but tricky puzzle, which implies that the answer has to be silly
    The fact that the author’s PhD friends could not solve this means that the usual methods of plotting and correlation probably won’t work.
    The key for me was that 8888 = 8. Two loops in the shape of each 8 times 4 = 8.
    Notice also that 9009=4 and 9900=4 which would cause you to suspect that the positions of the 9’s and 0’s are not important.
    Then look at 9900=4 and 9910=3. You could strongly make the case that 0 in position 3 is worth 1.
    Then look at 9889=6. If 8’s are worth 2 in any position then two 9’s are worth 2 or 1 each.
    So then look at the 0 value 7172=0. If you go with the guess that we are adding the mapped value of each of the four digits then you could make the guess that 7’s, 1’s and 2’s in any position are worth 0. This theory actually works out. So continue along this way.
    So 3859=3 because the number 8 has 2 loops and 9 has 1 loop.

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