✔ 最佳答案
a)C(contain no vowels)=C(the first is consonant)xC(the second is consonant)xC(the third is consonant)xC(the fourth is consonant)xC(the fifth is consonant)
=21x21x21x21x21=21^5=4084101
b)C(start with a vowel)=C(the first is vowel)xC(the second to fifth are consonant)
=5x2^4=972405
c)C(at least one vowel)=All combination-C(conatin no vowels)
=26^5-21^5=7797275
d)C(begin with B or end with H)
=C(the word begins with B)+C(the word end with H) -C(begin with B and end with H)
=(1)x(26^4)+(26^4)x(1)-(26^3)
=896376
e)C(start with C and contain at least one vowel)
=C(first letter is C)xC(the remaining letters contain at least one vowel)
=(1)x(all combination of 4 letters - C(the remaining 4 letters contain no vowels)
=26^4-21^4=262495