Suppose, the six-digit number is denoted by a1a2a3a4a5a6
For the number to be greater than 4,00,000,
a1 should be either 4 or 5.
If a1 is 4, then a2a3a4a5a6 can be arranged in 5!2!=60 ways
If a1 is 5, then a2a3a4a5a6 can be arranged in 5!2! 2!=30 ways
∴ Total number of required numbers =90