This is a problem of " inclusion-exclusion principle " . Robert Gentel was right in realizing that if one has guessed 3 fruits correctly then that person
has also guessed 4 fruits correctly ; tough Gentel ' s answer was wrong .
If y number of people have guessed 3 fruits correctly then ,
123 = 43 + 39 - 31 + 4y - y i.e. 3y = 72 i.e. y = 24 is the answer .