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out of 7 consonants and 4 vowels, how many words each containing 3 consonants and 2 vowels can be formed?
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The condition says nothing about repeating/non-repeating letters. I will consider the case when repeating is NOT allowed.
We can select 3 different consonants out of 7 by ways;
We can select 2 different vowels out of 4 by ways;
We can order any 3+2 = 5 letters word by 5! = 120 ways.
So, the number of ways in this case is equal to ...