To the zoo
Probability
Level
3
A teacher takes 3 children from her class to a zoo at a time,but she does not take same three children to the zoo more than once.She finds that she went to the zoo 84 times more than a particular child has gone to the zoo.The number of children in her class is
12
60
10
30
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The number of times the teacher goes to the zoo =nC3
The number of times a particular child goes to the zoo=(n-1)C2
From the question
nC3-(n-1)C2=84
(n-1)(n-2)(n-3)=6×84 =>9×8×7 =>n-1=9 =>n=10