The number of 6 -digits has two pairs of digits and 2 different digits. The number of ways of selecting 2 digits for two pairs and 2 other digits =‌4C2×‌2C2. Now, we arrange these six digits which consists of two pairs and 2 differentdigits. This can be done in ‌
6!
2!2!
ways. ∴ Required number of numbers =‌4C2×‌2C2×‌