Out of seven consonants and 4 vowels, how many words of 3 consonants and 2 vowels can be formed ?

Number of ways of selecting (3 consonants out of 7) and (2 vowels out of 4) =(  $C37\times C24$ ) = 210.

Number of groups, each having 3 consonants and 2 vowels =210

Each group contains 5 letters.

Number of ways of arranging 5 letters among themselves = 5! = 120. 

Required number of words = (210 x 120) = 25200.