There are 1000 junior and 800 senior students in a class.And there are 60 sibling pairs where each pair has 1 junior and 1 senior. One student is chosen from senior and 1 from junior randomly.What is the probability that the two selected students are from a sibling pair?
845 / 50000
714 / 80000
741 / 40000
854 / 50000
Explanation:
Junior students = 1000
Senior students = 800
60 sibling pair = 2 x 60 = 120 student
One student chosen from senior = 800C1
=800
One student chosen from junior=1000C1=1000
Therefore, one student chosen from senior and one student chosen from junior n(s) = 800 x 1000=800000
Two selected students are from a sibling pair n(E)=120C2=7140
therefore,P(E) = n(E) / n(S)=7140/800000
= 714/80000
Junior students = 1000
Senior students = 800
60 sibling pair = 2 x 60 = 120 student
One student chosen from senior = 800C1
=800
One student chosen from junior=1000C1=1000
Therefore, one student chosen from senior and one student chosen from junior n(s) = 800 x 1000=800000
Two selected students are from a sibling pair n(E)=120C2=7140
therefore,P(E) = n(E) / n(S)=7140/800000
= 714/80000