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4:50 AM
A classroom of 20 students can be categorized on the basis of blood-types: 5 students each
with “A”, “B”, “AB”, and “O” blood-types. If four students are selected at random from
this class, what is the probability that each student has a different blood-type?
Explain me each and every step for such problem
 

« first day (306 days earlier)