4
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I saw this puzzle many moons ago and so I assumed it would already be on here somewhere. I have looked and not found, though, and so I present to you a puzzle that baffled me when first I saw it.

What number replaces the question mark in the last example and why?

3531 → 0
3597 → 1
3891 → 3
9397 → 2
3869 → 4
2128 → 2
3786 → 3
3506 → 2
2700 → 2
7212 → 0
7205 → 1
2990 → 3
9503 → 2
1057 → 1
1160 → 2

1995 → ?

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  • $\begingroup$ Good find. I couldn't find a duplicate when I looked but I believe you're right. $\endgroup$
    – Engineer Toast
    Commented Mar 7, 2015 at 23:45

2 Answers 2

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4
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It is

2

You count the amount of

enclosed areas in the numbers

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  • $\begingroup$ That certainly didn't take long and this is the kind of elementary answer I expected. $\endgroup$
    – Engineer Toast
    Commented Feb 9, 2015 at 14:02
  • $\begingroup$ Not sure why the other answer is so much more popular. It's pretty much the same thing as this, but without making the connection with what you're actually counting. $\endgroup$
    – glibdud
    Commented Feb 23, 2015 at 19:51
  • $\begingroup$ @glibdud The other answer is more mathy. The masses have spoken on which is regarded as more clever. This answer more accurately meets the intent of the question, though. $\endgroup$
    – Engineer Toast
    Commented Feb 24, 2015 at 17:17
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The answer provided by Mathias711 is correct, however there is an alternate and lengthier solution to this problem.

We can assign the number values....

Like from 3531 = 0 and 7212 = 0, we can say that the digits 3,5,1,7& 2 have NO VALUE

Using this information we can get the value of 9

As 3597 = 1, and the fact 3,5&7 have no value, we can say 9=1 (i.e 9 has a value of ONE)

Similarly we can figure out the values of all digits, however we don't need to as we already have enough information to get the answer....

1995= 2 (as 1&5 have no value and 9 has a value of ONE, hence two 9's will be 2)

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    $\begingroup$ Excellent mathematical solution. This is the adult-level answer. $\endgroup$
    – Engineer Toast
    Commented Feb 9, 2015 at 14:05
  • $\begingroup$ +1 for a purely mathematical not-outside-the-box answer. $\endgroup$
    – dmg
    Commented Feb 9, 2015 at 14:05
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    $\begingroup$ Ironically, using this method, we still have no idea what value: 4444 would be ;) lol $\endgroup$
    – Ditto
    Commented Feb 9, 2015 at 14:24
  • $\begingroup$ @Ditto But no one cares as it is not in the problem statement. Technically even with the original method, you could not be certain as 8, 6 and 9 have circle(ish) parts, while 4 is more like a triangular. $\endgroup$
    – dmg
    Commented Feb 9, 2015 at 14:41
  • $\begingroup$ @dmg Exactly!!! :P :) $\endgroup$
    – The Dragonista
    Commented Feb 12, 2015 at 13:25

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