Answer:
11 times
Step-by-step explanation:
Number of apartment = 100
Number of times to screw on number 8
If the rooms are to be numbered from 1 to 100 ;
Then ; 8 will appear on the :
8th, 18th, 28th, 38th, 48th, 58th, 68th, 78th, 88th, 98th
Counting the number of 8's = Eleven 8's
Number of 8's = 11 times