A drawer principle problem, but also analysis The summer camp organizes activities for 200 students, including visiting famous schools, surfing on the sea and mountain climbing. It is stipulated that each student must participate in one or two activities, so how many students participate in the same activities at least?

A drawer principle problem, but also analysis The summer camp organizes activities for 200 students, including visiting famous schools, surfing on the sea and mountain climbing. It is stipulated that each student must participate in one or two activities, so how many students participate in the same activities at least?

1. Types of participation: (3 + 3 = 6)
a. Visit famous schools;
b. Surfing on the sea;
c. Mountain climbing;
d. Visit famous schools and surf on the sea;
e. Visit famous schools and climb mountains;
f. Surf on the sea and climb mountains;
2. 200 △ 6 = 33 (Times) 2 (pieces)
33 + 1 = 34
Because there are six kinds of participation, if we arrange it according to different kinds, 33 of the 200 students will participate in the same project, and there are still two students left. No matter how you arrange, at least 34 students will participate in the same project
3. Please remember that the solution to the drawer principle is:
First, list the different types in the question one by one, and see how many kinds there are. Second, see how many different types are included in the total number of the answers, and several of them are the same. Third, don't forget the remainder. No matter what the remainder is, add 1 to the number of repetitions (this is the key)

A drawer principle problem
There are 90 balls in a box, of which 20 are red, 20 are yellow and 20 are green, and the rest are 15 black balls and 15 white balls. These balls are only different in color. If you want to take out 10 balls of the same color in the dark, how many balls should you take at least

If there are five colors, then if you take 5 × 9 + 1 = 46 balls, you will get 10 balls of the same color

When you touch the ball from the bag containing 77 balls of 7 colors, you can't judge the color. To ensure that the ball is filled with 7 boxes, 7 balls in each box, and the balls in the box are the same color, you need to touch at least () balls
A. 85B. 84C. 71D. 50

78 + 7 = 85. So choose a