George said if 2 and 4 are factors of a number, then 8 is a factor of the number. is he correct explain?

Not always. Here's a statement that proves it wrong. 2 and 4 are a factor of 12. However, 8 is not a factor of twelve. In some cases though, it's right. 2 and 4 are a factor of 32. So is 8. So George is incorrect, it can only happen sometimes. Hope this helps. 

This is sometimes true.

2 and 4 are factors of 12 and 36.
8 is not a factor of 12 and 36.

2 and 4 are factors of 24 and 48.
8 is also a factor of 24 and 48.

George's statement is only sometimes true.