a) Let us first find out the total number of numbers. There are 99 as it is a pattern going up by 1s starting on 1.
To solve this problem, the first thing I did was to separate the 1-digit and 2-digit numbers. We know that the only 1-digit numbers are 1-9, and everything else is 2-digit numbers.
Let us list this information:
1-digit = 9x
2-digit = 90x (99-9)
Now to find the total number of digits, we can multiply the number of x-digit numbers by x.
\(9\cdot1=9\) (1-digit total)
\(90\cdot2=180\)(2-digit total)
\(9+180=189\)(total)
Sam wrote down 189 digits in total.
b) For this one, to find the probability of getting a 0 out of all digits, we can divide the number of 0s by the total number of digits.
As there are only a few 0s, we can list them out:
10,
20,
30,
40,
50,
60,
70,
80, and
90.
In total, there are 9 0s.
As we have already evaluated the total number of digits in part a), we can divide 9 by 189.
The probability that Sam chooses a 0 is 9 out of 189. (I think you should be able to do some simplifying yourself???)
c) I am so sorry, I'll come back to this question in about 20 mins, but I don't have time right now to explain it in detail.
However, I can tell you that it has something to do with this:
\(1+99\),
\(2+98\),
\(3+97\)...
\(49+51\),
\(50\)
I hope you will be able to solve it from here, but if not, I'll be back.
Hope this helped,