The 4 quadruples are complete, however the 5:th one is not. Replace the question mark. (All 5 quadruples follow the same rule)
1 Answer
50 ? Seems that third and fourth digit are multiples of first and second digit with common factor.
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$\begingroup$ This is the intended answer. I thought of it like this though: ad = bc. But since your reasoning obviously leads to the same answer, im giving you the tick :) $\endgroup$ Feb 11, 2020 at 14:51