How many four-digit numbers less than 6000 can be formed using the digits 2, 4, 6, 7, 8, and 9 with replacement? (i.e. digits can be repeated in the number, for example 2447 is acceptable.)
You can choose the first digit as either 2 or 4. That's 2 ways
to choose the first digit.
For each of those ways, you can choose the second digit any
of the 6 ways.
For each of those ways, you can choose the third digit any
of the 6 ways.
For each of those ways, you can choose the fourth digit any
of the 6 ways.
So the total number is 2x6x6x6 = 432 ways
Edwin