Question 372507
So he needs the final three digits.
The first digit can be from 0-9.
The second digit can be from 0-9.
The third digit can be from 1-9 since he knows it's not a 0.
In total, then the numbers can be,
{{{N=10*10*9=900}}}numbers
If each number takes 23 seconds, then
{{{T=900*23}}}
{{{highlight(T=20700)}}}seconds.
There are 3600 seconds in 1 hour,
{{{T=5.75}}} hours or 5 hours and 45 minutes.