Question

I really need help with this one...

Answer 1

From 100 to 999, how many digits have at least one zero?
From 100 to 999, how many number are there?

To answer the first question, let's look at all numbers in the 100's that have at least one zero.
100
101
102
103
104
105
106
107
108
109
110
120
130
140
150
160
170
180
190
There are 19 of them.
There are also 19 of them in each of the 200's, 300's 400's 500's, 600's, 700's, 800, and 900's.
That means there are 9 * 19 = 171

Now we need to answer the second question.
How many numbers are there from 100 to 999?
There are 900 numbers.

Now divide the first number by the second number:

171/900

Answer 2

well we have 101,102,103,104,105,106,107,108,109,110,201, etc. to 1000 so thats 90 right there. Then we have the multiples of ten excluding 100, 110, 210, etc.(we already "used" those) so we have 8*9-1 so we have 71 there thus it's D