+0  
 
0
75
2
avatar+529 

How many three-digit positive integers exist, all of whose digits are 2's and/or 5's?

Logic  Oct 9, 2018
 #1
avatar+92505 
+1

222

225

252

255

522

525

552

555

 

 

cool cool cool

CPhill  Oct 9, 2018
 #2
avatar+2294 
0

Listing all the possible arrangements is one way to approach this problem; however, if I told you that this number has 10  or 100 digits, would you be as willing to write out all of them? I doubt it.

 

The first digit has two possibilities; it can either be a 2 or a 5. 

 

The second digit has two possibilities; it can either be a 2 or a 5.

 

The third digit has two possibilities; it can either be a 2 or a 5.

 

\(2*2*2=8 \text{ integers}\)

TheXSquaredFactor  Oct 9, 2018

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