Any odd number plus an odd number will give an even result. Any even number plus an even number will give an even result.
Any odd number plus an even number will give an odd result.
This is actually pretty easy, you should be able to work it out yourself.
I take it that you want to make three digits numbers with 8,7,3, and 6 without repetition. The first digit cane be selected from among 4 digits, the second from 3 digits, the third digit from 2, hence the number of three digit numbers that can be formed without repetition is 4 x 3 x 2 = 24
100,000
12
24
There are 504 such numbers.
512
There are 900 of them.
27 three digit numbers from the digits 3, 5, 7 including repetitions.
48 of them if digits may not be repeated. 100 if they can.
Any 3 out of 4 = 4. Each set can be arranged 6 ways so 24 different numbers.
9999
I take it that you want to make three digits numbers with 8,7,3, and 6 without repetition. The first digit cane be selected from among 4 digits, the second from 3 digits, the third digit from 2, hence the number of three digit numbers that can be formed without repetition is 4 x 3 x 2 = 24
81 As there are no limits stated then you can have a number comprising a repeated single digit (such as 2222), two pairs of numbers (e.g. 2244) or three different numbers (such as 2462). The first digit can be one of any of the 3 numbers. The second digit can be one of any of the three numbers, as can the third digit and also the fourth. Then you can have 3 x 3 x 3 x 3 = 81 different 4-digit numbers using the three given numbers.
100,000
12
Choose from 4 for the first number, 3 for the second number, and 2 for the third number. Therefore there are 4*3*2 = 24 three digit numbers can be formed from 3769 if each digit is used only once.
24