The word RIPPLE has 6 letters. 


There are 5 and only 5 different (distinguishable) letters. Two letters (P) are identical.


Although there are formally 6! = 720 permutations/arrangements, not all of them are distinct/distinguishable.


Namely, in each permutation two identical letters P can be reversed in their positions, but the resulting permutations 
still represent the same arrangement.


Therefore, the whole number of permutations must be divided by 2 to account for this fact.


As a result, the final formula for the number of arrangements in this case is   = 360.