JEE Main 2024 Mathematics question
The number of 3-digit numbers, formed using the digits 2, 3, 4, 5 and 7, when the repetition of digits is not allowed, and which are not divisible by 3, is equal to .
Answer: 36
Solution
Total 5 × 4 × 3 = 60. Digit triples with sum divisible by 3: {2, 3, 4}, {3, 5, 7}, {2, 3, 7}, {3, 4, 5}: 4 × 6 = 24. So 60 − 24 = 36.