A digital safe opens only when you enter a four-digit number where the first digit is half the second, the third digit is the sum of the first and second, and the fourth digit is twice the second. The digits are all unique and non-zero. What is the code?
2468
Let the digits be W, X, Y, Z. W is half of X (W = X/2). Y is W + X. Z is 2 * X. Since digits must be unique and non-zero, let's test X = 4. Then W = 2, Y = 2 + 4 = 6, and Z = 2 * 4 = 8. The digits are 2, 4, 6, 8, all unique and non-zero. The code is 2468.
About this riddle
Logic riddles give you a few facts and ask what must be true. List what you know, cross out what cannot be, and see what is left.
Difficulty: Medium. More like this: Logic riddles with answers or try Einstein's Logic Grid for a different kind of puzzle.
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