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There are 24 table tennis balls in one box 1. If two-thirds of the students are sent, how many are left? 2. If you send one sixth of the whole box to the students first, and then one third of the whole box to the students, how many will be sent to the students?
1. 24 * (1-2 / 3) = 8
2. 24 × 1 / 6 + 24 × 1 / 3 = 12
There are the same number of table tennis and badminton in the box. Five table tennis and three badminton balls are taken out each time. After several times, the table tennis is just gone, and there are six badminton balls. There were () table tennis and () Badminton balls in the original
A. 3B. 15C. 18D. 45
Take the number of times 6 (5-3) = 3 (Times); table tennis number: 5 × 3 = 15 (Times); badminton number: 3 × 3 + 6 = 15 (Times); answer: table tennis and badminton each 15
Put 28 balls in different boxes. Each box has the same number of balls, more than one. How many boxes do you need? How many ways do you have?
The four methods need 24714 boxes respectively
Put 20 ping-pong balls into five different boxes. The number of balls in different boxes is different, and the boxes are not empty. There are several ways to pack them
First of all, let's see how many classification methods (combinations): 1) 10,1,2,3,4 (the maximum is 10) 2) 9,1,2,3,5 (take one from 1's "10" can only be put in "4") 3) 8,1,2,4,5 / 8,1,2,3,6 (take one from 2's "9" can be put in "3" or "5") 4) when the final maximum is 7, according to the result analysis of 3), there are: 7
Red, yellow, blue three colors of the ball each 10 into a bag, at least take how many balls, can guarantee to get two same color ball?
3 + 1 = 4 (pieces) because when each ball touches one, there will be three balls. If you touch another ball, there will be two balls of the same color, so there are four balls
There are red, yellow and green balls in the pocket
Among them, red ball accounts for 1 / 3 of the total number of balls, yellow ball accounts for 1 / 3 of the total number of balls, green ball is 50 more than yellow ball
x+50
An opaque bag contains 100 balls of red, yellow and white
Except for the color, they are all the same, in which the number of yellow balls is twice that of white balls, less than 5. It is known that the probability of finding a red ball from a bag is 310
(1) Find the number of red balls in the bag;
(2) Find out the probability that a ball is white from the bag;
(3) After taking 10 balls (no red ball among them), find out the probability that one of the remaining balls is a red ball
Test site: probability formula
Analysis: (1) according to the common number of red, yellow and white balls multiplied by the probability of red balls;
(2) Suppose there are x white balls and (2x-5) yellow balls. According to the meaning of the question, the equation is listed to find out the number of white balls and divide it by the total number of balls;
(3) First find out the number of balls left after taking 10 balls, then divide the number of red balls by the number of balls left
(1) According to the meaning of the title:
100×310=30,
A: there are 30 red balls
(2) Suppose there are x white balls, then there are (2x-5) yellow balls,
According to the meaning of the title, x + 2x-5 = 100-30
The solution is x = 25
So the probability that a ball is white is p = 25100 = 14;
(3) Because after taking 10 balls, there are 90 left, and the number of red balls has not changed,
So the probability of finding a red ball from the remaining balls is 3090 = 13;
A bag of red, orange, yellow three colors of the ball, each arbitrary touch 2, then at least a few people to ensure that there are two or more people choose the same ball
6 + 1 = 7 (people); answer: at least 7 people can guarantee that two or more people choose the same ball
There are 10 red, yellow and white balls in one bag. At least feel them out______ Only four balls can guarantee the same color of four balls
3 × 3 + 1 = 10 (pieces); answer: at least 10 can guarantee that four balls have the same color
There are 10 red, yellow and white balls in one bag. At least feel them out______ Only four balls can guarantee the same color of four balls
3 × 3 + 1 = 10 (pieces); answer: at least 10 can guarantee that four balls have the same color
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