Question

高手请帮忙解答一下 ><

以下是我不会的英文数学问题 厉害的高手 请帮我解答一下问题 拜托了

1 Heather asks three friends if they were born on a weekday or at the weekend.
a) Construct the probability tree diagram for this situarion
b) What is the probability that Heather’s friend were all born at the weekend ?
c) What is the probability that none of her three friends was born at the weekend ?
d) What is the probability that one of her three friends was born at the weekend ?
3.In a random experiment , the probability of an event A is 0.2 , and that of an event B , 0.3. what is the probability of :
a) A U B if A and B are mutually exclusive ?
b) A U B if P(A n B) = 0.18 ?
c) Pa (B) if P(A n B) = 0.18 ?

Answer 1

第一题：已知条件是出生在weekday的概率是5/7，在weekend的概率是2/7。
a)画出所有可能性下概率的树形图，这个很容易。如：A weekday, B,C都是weekend，概率是5/7*2/7*2/7=20/343；AB都是weekday，C是weekend，.......；其他情况。。。。。
那么有了上图，b,c,d的答案就都有了，如b的答案就是8/343。

另一题：看不懂符号，学过都忘了。

追问

c 和 d 的答案是什麼?

那个树型图 你能再解释清楚吗

因为我看不懂你说的 我不知道该怎麼画 首先分三条线 A B C ? 是这样吗?

追答

如图： B weekend 2/7 : C weekend 2/7 8/343
C weekday 5/7 20/343
A weekend 2/7: B weekday 5/7: C weekend 2/7 20/343
C weekday 5/7 50/343

B weekend 2/7 : C weekend 2/7 20/343
C weekday 5/7 50/343
A weekday 5/7: B weekday 5/7: C weekend 2/7 50/343
C weekday 5/7 125/343
所以c的答案是125/343，d的答案是50/343+50/343+50/343=150/343。