Find all three-digit numbers which decrease 13 times when the tens' digit is suppressed.
Solution
Let be such a number. The condition is , that is , same as . We notice that divides both and , so is divisible by , hence .
If , then . Since is a non-null digit, , and , which lead to the solutions , and .
If , then . Since is a non-null digit, the only possibility is , which leads to the solution .
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