10. Combinatorics & Probability
Combinatorics
Multiple Choice
Multiple ChoicePhone numbers are 10 digits long. How many possible phone numbers are there if the 1st and 4th numbers can't be 0?
A
10
B
90
C
8,100,000,000
D
10,000,000,000
101
views
Phone numbers are 10 digits long. How many possible phone numbers are there if the 1st and 4th numbers can't be 0?
10
90
8,100,000,000
10,000,000,000