Mr. W wants to divide a class of 20 students into 5 groups of 4 for a same task. In the class, Peter and David are twin

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Mr W Wants To Divide A Class Of 20 Students Into 5 Groups Of 4 For A Same Task In The Class Peter And David Are Twin 1 (161.33 KiB) Viewed 33 times

Mr. W wants to divide a class of 20 students into 5 groups of 4 for a same task. In the class, Peter and David are twin brothers and they may switch groups for fun because no one can tell them apart. How many ways are there to group the class if the twin brothers are not in the same group but John and Mary must be in the same group? (3A)