Could any1 help me a bit with this equation ?

1) X1+X2+X3=11 , So how many are the solutions?

2) We 've got these letters -> A,B,C,D,E,F,G,H , how many permutations

of these letters can we make that include ABC ?

3) How many ways are possible in order 3 girls and 8 boys sit in a row so that Mary and John NOT to sit next to each other ?

4) I can understand at all what this question wants, but anyway ill ask here maybe you can understand ...

How many bytes exist with 1) Exactly 2 aces

2) Exactly 4 aces

3) Exactly 6 aces

4) At least 6 aces

i dont get it , a byte consists of 8 bits, whats that ace? any ideas?

Thanks in advance for your help =)