Answer:
1 digit: 4 digits (1, 3,5,7)
Two digits: 12 (13, 15, 17 ...)
Therefore, 16 1 or 2 digits can be used.
2. The telephone number consists of 8 digits, the first digit is 9, the second digit is 3, 4, 5 or 8, and the rest digits are not limited. How many such phone numbers are there?
Answer:
1*4* 10^6=4* 10^6
3. If repetition is allowed, how many four-digit numbers can be formed by using the numbers 1, 3, 5, 7, 9 and 2?
Answer:
6^4= 1296
The TV station held a cricket match called "Best Catcher". The six selected catchers, A to F, are arranged in a certain order for the audience to judge. Q * * * How many permutations are there?
Answer:
P6, 6=720(Px, y means selecting y from x numbers to arrange)