JEE Advanced Mathematics question
A teacher takes 3 children from her class to the zoo at a time as often as she can, but she does not take the same three children to the zoo more than once. She finds that she goes to the zoo 84 times more than a particular child goes to the zoo. The number of children in her class is
Answer: (B)
Solution
Let the class have children. "As often as she can" without repeating a trio means she takes every possible trio once, so she goes times. A particular child goes once for every trio containing them:
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