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We call a number peachy if every digit in the number is either a 3 or next to a 3 For example, the numbers 333, 83, 303 and 3773 are all peachy, but the numbers 32523, 786, 340 and 3999 are not peachy.

How many positive 2 digit numbers are peachy?

 Feb 22, 2021
 #1
avatar+939 
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Here's a hint: count all the numbers that are not peachy then subtract from all the 2 digit numbers.

 Feb 22, 2021
 #3
avatar+36 
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Complementary counting! laugh

AnxiousLlama  Feb 22, 2021
 #2
avatar+36 
+1

Here is a massive hint! laugh

 

Any 2-digit number with a 3 is peachy (and all peachy numbers have at least one 3). There are nine 2-digit numbers with ones digit 3, and there are nine additional 2-digit numbers with tens digit 3 (except from 33, which we've already counted, since its ones digits is 3). Therefore, there are . . .

 Feb 22, 2021

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