Some three digit numbers are divided by 3.5.7 to make up 2. Arrange these three digit numbers from small to large, and the fourth number is

Some three digit numbers are divided by 3.5.7 to make up 2. Arrange these three digit numbers from small to large, and the fourth number is

The least common multiple of 3, 5 and 7 is 105, so these three digits are the integral multiple of 105 plus two
The fourth number is 105 * 4 + 2 = 422

After the nine numbers 1, 2, 3 and 9 are written in a row in any order, the three adjacent numbers can form seven triples according to their order in the arrangement
For each permutation of 1 ~ 9, sum the corresponding seven three digit numbers, then the minimum value of the sum of these three digit numbers is, and the maximum value is
To write a specific process!
I'm wrong, please tell me!

123456789
Among them, 34567 was used three times, 28 twice and 19 once
To make the maximum: 999 + 888 + 777 + 666 + 555 is the maximum, 442 + 321 is the remaining maximum
So: 34 (middle 5 random row) 21, such as 345678921, at this time and 4648
To make the minimum: 111 + 222 + 333 + 444 + 555 is the smallest, 668 + 789 is the smallest remaining row
So: 76 (middle 5 random row) 89, such as 761234589, at this time and 3122

You can make up () different three digit numbers with 2, 3 and 5. Arrange these three digit numbers from small to large, and the number in the second place is ()
There are four students, every two people talk on the phone, a total of how many times? If each of them gave each other a card, how many cards did they send?

1. (3 × 2 × 1 = 6) different three digit numbers can be made up of 2, 3 and 5
Put these three digits in the order from small to large, and the second number is 253
2. There are four students, every two people talk on the phone, a total of: 4 × 3 △ 2 = 6 times or: 3 + 2 + 1 = 6 times
Greeting cards: 3 × 4 = 12