论文部分内容阅读
(2005年全国高考江苏卷第20题)甲、乙两人各射击一次,击中目标的概率分别是2／3和3／4。假设两人射击是否击中目标,相互之间没有影响；每次射击是否击中目标,相互之间没有影响。 (1)求甲射击4次,至少1次未击中目标的概率； (2)求两人各射击4次,甲恰好击中目标2次且乙恰好击中3次的概率； (3)假设某人连续2次未击中目标,则停止射击。问乙恰好射击5次后,被中止射击的概率是多少? 注意一“至少”类问题的分解与转化对于“至少”类问题,一般有两种处理方法：一是分解成若干个互斥事件的和；二是转化为其对立事件,利用P(A)=1-P(A)求解。
(2005 issue 20 of the National College Entrance Examination in Jiangsu Province) Both A and B shot once, and the probability of hitting targets was 2/3 and 3/4 respectively. Assume that if the two men shoot at the target, they have no effect on each other; whether or not each shot hits the target has no effect on each other. (1) Find the probability that A fires 4 shots at least 1 time without hitting the target; (2) Find the shots of the two shots 4 times, A hits the target exactly 2 times and B just hits 3 times; (3) Suppose someone has missed the target for 2 consecutive times, then stop firing. The probability of being fired after Q2 is fired exactly 5 times? Note the decomposition and transformation of the “at least” type of problem There are two general approaches to the “at least” type of problem: The first is to decompose into several mutually exclusive events. The second is to convert to its opposition event, using P(A)=1-P(A) to solve.