Regular Expression

Question

Is this regular expression is correct for the Language = { w| number of a's in the string = 0 mod 3} on $\Sigma=\{a,b\}$

Comments

Ans should be b*(b*ab*ab*ab*)b*

Answer 1

This is wrong what about string ababa how will you generate this.

It should be b*(b*ab*ab*ab*)*b*

And on other hand if you mean n(a)=0mod3 this means it should not contain any than its just b*

But if n(a)mod3=0 then the above one