Question

Let X be the set of the 26 lowercase English letters and 10 decimal digits. How many X-strings of length 15 satisfy all of the following properties (at the same time)?
A. The first and last symbols of the string are distinct digits (which may appear elsewhere in the string).
B. Precisely four of the symbols in the string are the letter ’t’.
C. Precisely three characters in the string are elements of the set V fa; e; i; o; ug and these characters are all distinct.

Answer 1

The correct answer is B

Answer 2

The answer is b cuz pre

Answer 3

For the first condition.
first and last symbols of the string distinct digits. are
Suppose that first digit we get=10
and the last digit we get = 9

For the second condition
Four of the symbols in the string letter 't' are the

We get t = 1
=1x1x1x1

For the Third condition.
We have to select three characters. from the given vowels V = {a,e,i,o,u}
In vowel five characters are there.
So we select 5, 4, and 3 = 5x4x3.

Finally

= 10x1x1x1x1x5x4x3x36x36 x 36 x 36 x 36 x36x9

Note: we have get 36 because of the,
there are character = 26 and 10 digits
26+10 = 36