Answer: There are 1400 different combinations.
Step-by-step explanation:
The conditions are:
we have 4-digits: abcd.
all the digits are different.
a is an odd number, and b is an even number.
Then, for a, we have the options 1, 3, 5, 7 and 9 (so we have 5 options).
for b, we have the options 0, 2, 4, 6 and 8 (so we have 5 options).
for c, we can have odd or even numbers, so we have 8 options ( remember that there where 2 numbers already taken away, this is why we have only 8 options).
for d we have 7 options (because 3 numbers are already taken).
Then the number of combinations is equal to the product of the number of options for each selection:
C = 5*5*8*7 = 1400
