Question

How many times is 25 written when listing all numbers From 1 to 100000?

Answer 1

Answer:

In this question, firstly I consider the set {0,1,2,3,4,6,7,8,9}, find the number of sequence whose length 2,3,4 and 5 and it contains 25, and then multiplied it with 2 since I should also consider the set {0,1,3,4,5,6,7,8,9}, which will give me the same number of different sequence, so I found the answer 5832

Answer 2

Answer

4000

Step-by-step explanation:

We may as well count the no.of occurrences of the substring 25 in the 100000 five digit strings 100000-99999. For each of the four possible positions of 25 in a five digit strings there are exactly 1000 strings where this occurrence is counted.