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Q.
The number of ways of placing 18 mice in two experimental groups and one control group, with all group equally large, are
Permutations and Combinations
Solution:
Number of ways of placing $18 mice$ in two experimental
groups and one control group $ ={ }^{18} C_6 \times{ }^{12} C_6 \times{ }^6 C_6 $
$ =\frac{18 !}{12 ! 6 !} \times \frac{12 !}{6 ! \times 6 !} \times 1 $
$ =\frac{18 !}{(6 !)^3}$