如何在一定比例的时间内生成随机数

I am trying to generate a random number that only populates a certain percent of the time. For example, I want to create an array that is set between a certain range (lets say 0-100), but 10% of the time I want the random number chosen to be multiplied by n. How would I be able to generate this "random" number n% of the time?I am trying to generate a random number that on