Anna and Mark are included in a group of 8 people. If 4 people are selected at random and without replacement from this group, what is the probability that Mark and not Anna will be selected?
a.1/7
b.2/7
c.3/7
d.4/7
e.5/7
OA: b
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Anna and Mark
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It is B
Suppose the combination of people selected is Mxxx
where x represents any person other than Anna
Probability of this combination = (1/8)*(6/7)*(5/6)*(4/5) = 1/14
Now Mark can be selected at 2nd, 3rd or 4th position too. so,
total probability = 4*1/14 = 2/7
Suppose the combination of people selected is Mxxx
where x represents any person other than Anna
Probability of this combination = (1/8)*(6/7)*(5/6)*(4/5) = 1/14
Now Mark can be selected at 2nd, 3rd or 4th position too. so,
total probability = 4*1/14 = 2/7
