A pet shop manager wants the same number of birds in each cage. He wants to use as few cages as possible, but can only have one type of bird in each cage. If he has 42 parakeets and 18 canaries. How many birds will he put in each cage

If he can only put one type of bird in each cage, he would have 18 cages full of 1 canary paired with 1 parakeet, and then 24 cages with a single parakeet in each. There is no way to have the same number of birds in each cage, unless there is a missing variable.