it is an iq question and i hope to find an answer ..

If it's an "IQ question", then surely the idea is that you work it out yourself?

25N+6
N is the number of candies she has at the end.

Poyla--how I solved it
What do I know she started with K pieces of Candy and had N at the end
She started with K pieces of candy
She ate 1, left with K-1 pieces
Gave 4/5 to sister, left with 1/5(K-1)
She ate another, left with 1/5(K-1)-1
Gave 4/5 to brother, left with 1/5[1/5(K-1)-1] or N pieces

N=1/5[1/5(K-1)-1]
5N=1/5(K-1)-1
5N+1=1/5(K-1)
25N+5=K-1
25N+6=K
She started with 24N+6 pieces

Most important part--check the answer
start 25N+6
ate 1 left with 25N+6-1=25N+5=5(5N+1)
gave away 4/5 left with 1/5*5(5N+1)=5N+1
ate another left with 5N+1-1=5N
gave avay 4/5 left with 1/5*5N=N

Rap