rakman123
The string of digits 135791113...999 is formed by merging together the decimal representations of the odd integers from 1 through 999. Counting from left, what is the 110th digit of this string of digits?
A) 0
B) 3
C) 5
D) 7
E) 9
A good one!
Let's visualize this
\(\quad1 \quad3 \quad5 \quad7 \quad9 \quad11 \quad13 \quad....\quad 997 \quad 999\)
This is an arithmetic sequence with a common difference = 2
We want to find the 110th digit of this string (counting from the left)
Length of the string contributed by the 1 digit number = 5 (i.e. 13579)
Each of the two-digit numbers will contribute a length of two to the string
Total length contributed by the two-digit numbers = Number of two-digit numbers * 2
Number of two-digit numbers =\(\frac{ (99 - 11) }{ 2 }+ 1 = 45 \)
length contributed by the two-digit numbers = 45 * 2 = 90
Total Length obtained so far = 90 + 5 = 95
Remaining length = 110 - 95 = 15
Each three-digit number will contribute a length of 3 to the string. Hence, we need \(\frac{15}{3} = 5\) three digit numbers.
101 103 105 107 10
9110th digit = 9
Option E