There are three red balls and two white balls in the pocket. The texture is uniform and the shape is exactly the same. Pick out two balls randomly from them. Calculate the probability that both are red balls. (list or tree chart)

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• 1. A person forgets the last number of the phone number. He dials randomly and asks for the probability that he can dial correctly no more than three times? A .1/10 B .1/8 C.3/10 You can use the formula of 9 / 10 * 8 / 9 * 1 / 8 to calculate that the final answer is equal to answer A. I know, but what bothers me very much is that if you add the question no more than three times, then if you add the question no more than nine times, then the probability is still 1 / 10 when you dial nine times. It's a bit inexplicable here. Some of the translations haven't been practiced yet
• 2. The probability of occurrence of a is 60, and that of B is 40. What is the probability of occurrence of at least one of AB? (1-60) * (1-40) is that right?
• 3. On the probability basic event space of mathematics compulsory 3 Take any 4 out of 50 products with 6 defective products, and observe the number of defective products. The basic event space is
• 4. For example: the event with probability 1 is not necessarily inevitable, and the event with probability 0 is not necessarily impossible
• 5. Probability of relatively independent events in Mathematics There are 10 balls from No.0 to No.9, which are pulled out one at a time and then put back. The probability of pulling 1 is 1 / 10, that is to say, there will be one in 10 times. Then I want to know the probability of pulling 1 only after 20 times and how much is it after 30 times
• 6. How to understand that an event with probability equal to 1 is not necessarily an inevitable event, and an event with probability equal to 0 is not necessarily an impossible event, please elaborate in detail and give examples
• 7. 9 (X-Y) ^ 2 + m + 4 is a complete square expression, and M expression is obtained
• 8. Given that M belongs to R, f (x) = (m-1) x ^ 1 / M is a power function. (1) the expression for finding f (x): (2) if f (2-A ^ 2) ≥ f (a), find the value range of real number a
• 9. As shown in the figure, in the plane rectangular coordinate system, the image of quadratic function y = x + BX + C intersects with X axis and points a and B, point a is on the left side of the far point, the coordinate of point B is (3,0), intersects with y axis and points c (0, - 3), and point P is a moving point on the parabola below the straight line BC 1. Find the expression of this quadratic function 2. Connect Po and PC, and fold △ POC along CO to get quadrilateral pop ˊ C. is there a point P to make quadrilateral pop ˊ C diamond?
• 10. What's the difference between free table and database in VFP? How many parts does a table consist of? What are the steps to create a table?
• 11. It is known that Party A and Party B are good friends. They agree to meet at the gate of Shanghai park from 9:00 to 10:00 one day. If one of them waits for 20 minutes within the agreed time and does not see the other, they will leave. If both of them fulfill their promise, what is the probability of the two good friends meeting?
• 12. Take any one of the four numbers from 1 to 4 as the numerator, and take any one of the three numbers from 2 to 4 as the denominator to form a fraction. What is the probability of a fraction with Coprime numerator and denominator?
• 13. There are five small cards of the same size, write 1,2,3,4,5 on them respectively, and then put them in the bag to mix well. Take three cards out of the bag each time, record the results, and then put them back into the bag to wash well. If there are three consecutive numbers, they are called "step height". For example, 1,2,3:2,3,4; 3,4,5. What is the probability of "step height"?
• 14. Mathematical problems about frequency and probability There are 30 employees in a certain unit. There are 6 tickets for the concert. The leader decided to give them to 6 employees. For the sake of fairness, he numbered the employees by 1 ~ 30 and generated them randomly with a calculator____ One____ The number between the integer and the random number is the same as the employee going to the concert I don't want only one answer, give me a process, OK? I want to really understand what this question means. Thank you!
• 15. The probability of event a happening in one experiment is 2 / 3, and the probability of event a happening twice in four repeated independent experiments is?
• 16. In the four independent repeated trials, the probability of random event a occurring just once is not greater than the probability of its occurring just twice, then the probability of event a in one trial
• 17. If the probability of event a occurring at least once in four independent repeated tests is 8081, then the probability of event a occurring in one test is 8081______ ．
• 18. What is the probability formula of independent events occurring simultaneously? What is the probability addition formula of mutually exclusive time? What are these probability formulas?
• 19. Let a and B be two independent events that cannot happen at the same time In an event, the probability of occurrence of a and B is 30%. A and B are independent of each other and cannot occur at the same time. What are the percentages of occurrence probability of a and B? What is the formula? A and B are mutually exclusive, that is to say, after a occurs, B does not occur, and B occurs, then a does not occur, so the probability of occurrence of a or B can not be 30%. If it is still 30%, then the total probability of occurrence of a or B should be 60%, and the probability of both not occurring is only 40%, which is obviously wrong
• 20. Fill in 35 × 56 = 1960 19.6 = () × () = () × ()