Question 595375
There are 10 single digit numbers: 0,1,2,3,4,5,6,7,8,9


Of these, only 2-9 can be used for the first digits. So there are 10-2 = 8 choices for the first slot.


The rest can use any of the ten listed above. 


From here, you simply multiply out the possible choices



(# of choices for first slot)*(# of choices for second slot)...(# of choices for last slot)


8*10*10*10*10*10*10 <<--- There are 6 copies of 10 being multiplied here


8*10^6


8*1,000,000


8,000,000



So there are 8,000,000 (eight million) possible phone numbers.


So the answer is choice C