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【简答题】
袋子中放有大小和形状相同的小球若干，其中标号为0的小球1个，标号为1的小球1个，标号为2 的小球n个，已知从袋子随机抽取1个小球，取到标号为2的小球的概率是 1 2 ． （Ⅰ）求n的值； （Ⅱ）从袋子中不放回地随机抽取2个球，记第一次取出的小球标号为a，第二次取出的小球标号为b． ①记“a+b=2”为事件A，求事件A的概率； ②在区间[0，2]内2个实数x，y，求事件“x 2 +y 2 ＞（a-b） 2 恒成立”的概率．
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举一反三
【单选题】The meeting is for the ______purpose of discussing how to prevent crime.
A.
detailed
B.
specific
C.
limited
D.
sophisticated
【单选题】Before the experiment ______.
A.
the four divisions were carefully selected to suit a specific programme.
B.
each division was told to reduce its level of productivity.
C.
the staff involved spent a number of months preparing for the study.
D.
the employees were questioned about their feelings towards the study.
【单选题】The word 'particular' in paragraph 3 is closest in meaning to _________.
A.
peculiar
B.
specific
C.
exceptional
D.
equal
【单选题】（ ） is a letter from a bank to a foreign bank authorizing the payment of a specified sum to the person or company named.
A.
Letter of Delivery
B.
Letter of Credit
C.
Letter of Indemnity
D.
Letter of Guarantee
【简答题】John forgot to ________( specif ic) the place where we should meet.
【单选题】There is still a ___________ doubt among them as to the practical value of the building. [ ]
A.
specific
B.
sure
C.
some
D.
certain
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