Other Topics Puzzle – Challenge 95
This great logic and critical thinking puzzle is based on logic and a bit of mathematics. Let's see who can solve it. The solution is also provided.
A book has 500 pages that is numbered from 1 to 500. How many numbers 2 is used for numbering all pages? (for page 222, three number 2 is used and for 201, one number 2 is used)
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The correct answer is C.
To answer this question, we need to find the pattern. From 1 to 10, there is one number 2. From 10 to 19 has the same situation. From 20 to 29, there are 11 number 2. Why? (Consider 22)
With the same method, there is one number 2 in every ten numbers from 30 to 100. So, there are 20 number 2 from 1 to 100. There are 20 number 2 from 100 to 199.
From 200 to 300, there are 120 number 2. Why? (all numbers from 200 to 299 begin with 2)
From 300 to 500 there are 40 number 2. Therefore, there are 200 number 2 from number 1 to 500.
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