Question

Lauren has a paper with a seven-digit phone number that has the last three numbers smudged so that she cannot see them. The first four digits are 1, 7, 9, and 8, and the last three digits are the ones she cannot discern. How many possible phone numbers must Lauren dial if she is to be certain the she will eventually dial the correct number?
A. 1000
B. 100
C. 10
D. 30

Answer 1

Answer: A. 1000

Step-by-step explanation:

The number of digits used to fill the three digits space (0,1,2....9) = 10

Since, she  cannot discern the last three digits, so there can be repetition of digits in the last three digits.

Therefore, the number of possible phone numbers must Lauren dial if she is to be certain the she will eventually dial the correct number=$10\times10\times10=1000$

Hence, the possible phone numbers must Lauren dial if she is to be certain the she will eventually dial the correct number = 1000