Use the nine numbers 1-9 to form prime numbers. If each number is used and can only be used once, how many prime numbers can these nine numbers form at most

Use the nine numbers 1-9 to form prime numbers. If each number is used and can only be used once, how many prime numbers can these nine numbers form at most

In order to make the nine numbers from 1 to 9 form the most prime numbers, each prime number must use the least number. Therefore, the prime number composed of one number is 2, 5, 7, and the prime number composed of two numbers is 61, 89, and 43. To sum up, the nine numbers can form up to six prime numbers, which are 2, 5, 7, 43, 61, and 89

How many groups of 4-digit passwords are there composed of 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9?

10*10*10*10=10000

Use 0-9 to form a six digit password. Someone forgets the last digit
(1) The probability that someone will be right if he presses a number no more than twice
(2) Remember the even number of cases T, not more than 2 times on the right probability

1) The probability that someone will be right if he presses a number no more than twice
9/10*1/9+1/10=1/5
2) Remember the even number of cases T, not more than 2 times on the right probability
4/5*1/5+1/5=2/5

Use 0, 4, 2, 5, 8, 7 to form different six digit numbers, the largest of which is______ The smallest number is______ The difference between two numbers______ ．

Using the six numbers of 0, 4, 2, 5, 8 and 7 to form a minimum six digit number is 204578, and the maximum six digit number is 875420; 875420-204578 = 670842; so the answer is: 875420204578670842