Marble Puzzle

There are 25 marbles of equal weight and one that weighs a little more. Given a balance, how many weighings are required to deduce which is the heavier marble?
solve in 3 iterations.
Divide into three groups

1st
8,8,9

if 8 and 8 are equal

then take 9

divide into three group
3,3,3

if 3 and 3 equal
again divide into three group
1,1,1

again weigh if two are equal third will be heavier.

If 8 and 8 are not equal

then divide 8 into three group

2,2,3

then  2 or 2 are equal then divide 3 into three group
1,1,1
again weigh if two are equal third will be heavier.

if 2 and 2 are not equal

then divide 2 into two group

1,1

again weigh 2nd or 1st  will be heavier.

-----
25
8,8,9
3,3,2
1,1

25
8,8,9
3,3,2

1,1,1

or
25
8,8,9
3,3,3
1,1,1