Answer:
5259544316
Step-by-step explanation:
Given that:
Length of string = 7
Either begins with 2 consonants or ends with 2 vowels :
Either or :
A U B = A + B - (AnB)
Number of vowels in alphabet = 5
Number of consonants = 21
2 consonants at beginning :
First 2 consonants, then the rest could be any:
21 * 21 * 26 * 26 * 26 * 26 * 26 = 5239686816
3 vowels at the end :
First 4 letters could be any alphabet ; last 3 should be vowels.:
26 * 26 * 26 * 26 * 5 * 5 * 5 = 57122000
2 consonants at beginning and 3 vowels at the end :
21 * 21 * 26 *26 *5* 5 * 5 = 37264500
Hence,
2 consonants at beginning + 3 vowels at end 2 consonants at beginning - 2 consonants at beginning and 3 vowels At end
(5239686816 + 57122000) - 37264500
= 5259544316
Hence, number of 7 alphabet strings that begins with 2 consonants and end with 3 vowels = 5259544316
