It takes 15 days for Party A to do it, 10 days for Party B to do it, now Party A does it alone for 5 days, then Party A and Party B cooperate to set up Party A to work for X days

Party A completes 1 / 15 of the work every day, and Party B completes 1 / 10 of the work every day
Then 1 - (1 / 15 * 5) = (1 / 15 + 10 / 1) x (x stands for the number of working days after working alone for 5 days)

If a unit wants to organize a basketball league match, the competition system is a single cycle form (every two teams have a match), and it plans to arrange 10 matches, then the teams participating in the match should have______ ．

Let's invite x teams to participate in the game, and get 1 + 2 + 3 + according to the title +X-1 = 10, that is, X (x − 1) 2 = 10, ∧ x2-x-20 = 0, ∧ x = 5 or x = - 4

To organize a basketball league, the competition system is a single round robin form (every two teams have a match). 15 matches are planned. How many teams should be invited to participate in the competition?

Let's invite x teams to participate in the game, and get 1 + 2 + 3 + according to the title +X-1 = 15, that is, X (x − 1) 2 = 15, ｜ x2-x-30 = 0, ｜ x = 6 or x = - 5. A: six teams should be invited to participate in the competition

In order to organize a basketball league match, the competition system is in the form of a single cycle, that is, every two teams have a match, and 28 matches are planned. How many teams should be invited to participate in the game
At the graduation party of the third year of junior high school, everyone gives each other a picture, a total of 90 pictures. How many people are there

(1) 8 teams
Let x (x-1) / 2 = 28, x = 8
(2) 10 people
Let x (x-1) = 90, x = 10

It takes 15 days for Party A to do it, 10 days for Party B to do it, now Party A does it alone for 5 days, then Party A and Party B cooperate to set up Party A to work for X days