Question

a) A password must be 8 characters long and contain only digits and lowercase English letters. How many different passwords contain at least one digit and at least one letter? b) How many different strings of length 10 containing only the letters a, b, and c start or end with a c? c) How many people must be selected to make sure 20 of them were born in the same month?

I need the answer a, b, c.
you have to annwer part C must

Answer 1

Soln (a) NfAt least one digit and at least one litter = N(Total) - N( There is no better or there is no digit) = (26 +1938 -4 (No letter) +W/ No digit)) to the tot - 368 - (109+ 268) 368 – 108-26 (b) N/starting or ending with c) =N/starting with () INfending with c) =N(starting and ending with C) = 3?+ 32-3 9+9-3 = 15 (c) of 19x12=228 people are selected then there is a chance that 12 sets of 19 people each have same birthday niont. But if we take I more, then we can make sure that thette is a set of 20 people having same birthday month. so the Answer should be 228 +1 = 229. ANS: (a) 368-10-268 (b) 15 (c) 229

In c part slight correction. Written "mont" in place of "month"