Quantitative Aptitude – Equation – How many integers in the set

Slot – 3 – Quantitative Aptitude – Equation – How many integers in the set

Q. How many integers in the set {100, 101, 102, …, 999} have at least one digit repeated?
Answer: 252

Solution:
Basically we have to find out 3 digits numbers with at least 2 digits repeated ,
So if all three repeated = 9 (111, 222, ….999)
2 , zeros repeated = 9 (100, 200…., 900)
Any two other digits repeated = 9C1 *3!*9 – 9 = 234
Thus total such numbers = 234+9+9 = 252

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