We use cookies to personalise content and advertisements and to analyse access to our website. Furthermore, our partners for online advertising receive pseudonymised information about your use of our website. cookie policy and privacy policy.
 
+0  
 
0
228
2
avatar+822 

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

 Oct 9, 2018
 #1
avatar+101739 
+1

222

225

252

255

522

525

552

555

 

 

cool cool cool

 Oct 9, 2018
 #2
avatar+2340 
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.

 

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

.
 Oct 9, 2018

13 Online Users

avatar
avatar