Replace phrases with words from a thesaurus. Probability of executing code

So I have most of the code down an accurate. The goal is to take phrases from a song and replace the words with synonyms from a thesaurus file. However, only a user designated % of the time(so not all words will be changed)

import random
newfile = open("/Users/fp790/Desktop/assignment 10/python-asg10-Roget-Thesaurus.txt","r")
justinfile = open("/Users/fp790/Desktop/bieber_baby.txt","r")
splitjustin = justinfile.read().split("\n")
newjustin = []
thesaurus = {}
splitdata = newfile.read().split("\n")
for x in range (len(splitdata)):
    line = splitdata[x].split(",")
    word = line[0]
    thesaurus[word] = line[1:]
print("Total words in thesaurus:",len(thesaurus))

chance = int(input("Enter a % chance to change a word: "))

for q in splitjustin:
    rannum = random.randint(1,10)
    r = q.split()
    for s in r:
        if s in thesaurus:
            if rannum <= chance /100:
                ran = len(thesaurus[s])

                ranlis = random.randint(0,ran - 1)
                t = q.replace(s,str.upper(thesaurus[s][ranlis]),1)
                newjustin += [t]
            else:
                newjustin += [q]

the thesaurus code is fine. However even when I set chance to 100 only a couple words are changed. I think my loop/random number logic might be off. How do I get it to execute only x% of the time?