how many 4 digit number can be formed from the digits 2,3,5,,6,7,8 if:

a.)each digit be only used once
b) how many are even?
c) how many are odd?
d) how many are greater than 25000?

a. 6 distinct digits available, each used once.

Four digit numbers:
first digit: 6 choices
second digit: 5 choices
third digit: 4 choices
fourth digit: 3 choices.
By the multiplication rule to multi-step experiments, the total number of possibilities is 6*5*4*3=360
b. Half of the 6 digits are even, so half of the numbers are even.
c. The other half is made up of odd numbers.
d. none (for four-digit numbers)