MathCastle
Counting & ProbabilitySuperchallengeConditional Probability, Independence & Bayes

Conditional Probability, Independence & Bayes · Superchallenge problem

An integer is chosen uniformly at random from {1,2,…,n}\{1,2,\ldots,n\}. Let AA be the event that it is divisible by 33 and BB the event that it is divisible by 44. For how many values of nn with 1≤n≤1001\le n\le100 are AA and BB independent, that is, P(A∩B)=P(A) P(B)P(A\cap B)=P(A)\,P(B)?