口袋中有n（n∈N*）个白球，3个红球．依次从口袋中任取一球，如果取到红球，那么继续取球，且取出的红球不放回；如果取到白球，就停止取球．记取球的次数为X．若P（X=2）= 730 ，则n的值为_1．

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口袋中有n（n∈N^*）个白球，3个红球．依次从口袋中任取一球，如果取到红球，那么继续取球，且取出的红球不放回；如果取到白球，就停止取球．记取球的次数为X．若P（X=2）= 30

7

，则n的值为____．

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阅读下面短文，掌握其大意，从每题所给的A、B、C、D四个选项中，选出最佳选项。
FOUND
Black wallet with some money.
Come to Room 502 in the evening, or call 9796788.
WANTED IMMEDIATELY
A boy or a girl to deliver newspapers
Pay: $ 10 per day
Hours: 3:30 a.m. to 8:30 a.m. from Mon. to Sat.
For more information
Call Mr. Jones on 8947659 Call Jeff on 3338651
SINGLES’(单身) CLUB
A club for single people looking for new friends.
Ages: 25-40
Activities: parties, swimming, concerts, dances, etc
We meet every Friday at 8:30 p.m.
28 Garden Street Tel: 7026449 E-mail: singleclub@yahoo.com

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