A lock requires a four-digit code. The third digit is double the first. The second digit is the sum of the first and third. The fourth digit is one less than the second digit. The sum of all four digits is 26. What is the code?
3968
Let the first digit be X. The third digit is 2X, the second digit is X + 2X = 3X, and the fourth digit is 3X - 1. Summing all four gives X + 3X + 2X + (3X - 1) = 9X - 1 = 26. Solving for X yields X = 3. Substituting X = 3 gives digits 3, 9, 6, and 8.
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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