1）Howmany1-or2-digitnumberscanbemadeusingthedigits1,3,5and7ifnodigitcanbeusedmorethanonce2）Phonenumbersconsistof8digits.Thefirstmustbe9.Theseconddigitcanbea3,4,5or8.Therearenorestrictionsontheremainingdig

Question

1）How many1-or2-digit numbers can be made using the digits 1,3,5and 7if no digit can be used more than once
2）Phone numbers consist of 8 digits .The first must be 9.The second digit can be a 3,4,5or 8.There are no restrictions on the remaining digits.How many different telephone numbers are possible
3）How many 4-digit numbers can be made from the numbers 1,3,5,7,9and 2 if the numbers can be repeated
4）A TV station run a cricket competition called Classic Catches.Six catches,A to F,are chosen dan viewers are asked to rank them in the same order as the judge.The number of ways in which this can be done:720 证明

Answer 1

1、在不重复的情况下,用数字1、3、5、7可以组成多少个一位或两位数?
Answer:
1-digit:4 numbers (1,3,5,7)
2-digit:12 numbers (13,15,17...)
so, 16 1-or 2-digit numbers can be made.
2、电话号码由8位数字组成,第一位是9,第二位是3、4、5或者8,其余数字没有限制,问这样的电话号码共有多少个?
Answer:
1*4*10^6=4*10^6
3、如果允许重复,使用数字1、3、5、7、9和2可以组成多少个四位数?
Answer:
6^4=1296
4、电视台举行了一场叫做“最佳捕手”的板球比赛.被选出来的六名捕手,A到F按照一定的顺序排列起来以便于观众评判.问共有多少种排列方法?
Answer:
P6,6=720(Px,y表示从x数中选出y个进行排列)