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how many of the first 10000 positive integers contain the digit pair "43" in that order

 Sep 2, 2023
 #1
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There are 20 "43" in the first 1000 as follows:


43, 143, 243, 343, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 443, 543, 643, 743, 843, 943==20 such numbers.

 

This pattern repeats for every 1000 up to 10,000 for a total of: 20 x 10 ==200 such numbers.


In addition to the above, there are 100 "43's" between 4300 and 4399 inclusive for a total of:


200 + 100 ==300 integers that contain "43" in that order.

 Sep 3, 2023

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