Bank locker password - 2

Probability Level 3

A code for a safe is a five digit number that can have a 0 at the first place. How many codes have at least one digit 7?


The answer is 40951.

Aswin T.S. by Aswin T.S. , 20, India

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Chew-Seong Cheong
Mar 18, 2016
  • Total number of combinations: N = 1 0 5 N=10^5
  • Number of combinations without 7: N 7̸ = 9 5 N_{\not{7}}=9^5
  • Number of combinations with at least a 7: N 7 = N − N 7̸ = 1 0 5 − 9 5 = 40951 N_7=N-N_{\not{7}}=10^5 - 9^5=\boxed{40951}
4 Helpful 0 Interesting 0 Brilliant 0 Confused

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...