For the first section, Party A and Party B cooperate for 4 hours, Party B and Party C cooperate for 6 hours, Party A and Party C cooperate for 2 hours, and Party B completes the rest work in 7 hours, and Party B completes the work in a few hours

For the first section, Party A and Party B cooperate for 4 hours, Party B and Party C cooperate for 6 hours, Party A and Party C cooperate for 2 hours, and Party B completes the rest work in 7 hours, and Party B completes the work in a few hours

1 / A + 1 / b = 1 / 4
1 / B + 1 / C = 1 / 6
1 / A + 2 / B + 1 / C = 1 / 6 + 1 / 4 = 10 / 24 = 5 / 12
1 / A + 1 / C = 5 / 12-2 / b
2 * (1 / A + 1 / C) = 2 * (5 / 12-2 / b) = 10 / 12-4 / b
1-2 * (1 / A + 1 / C) = 7 / b = 1 - (10 / 12-4 / b)
3 / b = 2 / 12
B = 18
B. do the work alone for 18 hours

The sum of any four consecutive numbers is 45, the sixth is 11, the 19th is 5, and the 44th is 20

Every four numbers are equal
That is, 1, 5 and 9 are equal
2、6、10、.
3、7、11.
4、8、12.
The sixth number is 11, which is equivalent to the second number is 11
The number 19 is 5, which is equivalent to the number 3 is 5
The number 44 is 20, which is equivalent to the number 4 is 20
So the first number is: 45-11-5-20 = 9
The number 210 (210 = 52 * 4 + 2), which is equivalent to the second number, is 11

By observing the following numbers: 1,2,4,8... We find that the ratio of each term from the second term to its previous term is the fourth of 2,5, - 15,45

Well, in the second sequence, the ratio of each number to the previous number is - 3, so the fourth number is - 135!