（2）?四边形ABCD是矩形，
??AED??FDC,?DE?AB?CD ············································ 3分
又?CF?DE,??CFD??A?90?, ················································· 4分
??ADE??FCD ······································································ 5分 ?AD?CF················································································ 6分
21、解：设买的铅笔为x支，买的钢笔为y支． ···················································· 1分 根据题意得:?x?y?200?0.2x?5y?280 ① ?②
····················································· 3分
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解得??x?150 ··················································································· 5分
?y?50答:略 ································································································ 6分
22、解：?x1?x2?4,x1x2?2 ······································································· 2分
（1）
11x1?x24····························································· 4分 ????2 ·
x1x2x1x22（2）(x1?x2)2?(x1?x2)2?4x1x2?42?4?2?8 ·································· 6分
23、解：（1）略 ···························································································· 3分
（2）略 ····························································································· 5分 （3）15000?0.05?750（人） ····························································· 6分
?B的频率为0.2?0.31?0.51，大于A、C、D的频率，故这名学生评为B等的可能性最
大． ···························································································· 8分 24、解：（1）连结OC，?AB?4,?OC?2, ?PC为?O的切线，?CPO?30?,
M A P C OC2??23. ?PC? ············ 4分
tan3?033O B （2）?CMP 的大小没有变化 ································································ 5分 ??CMP??A??MPA··································································· 6分
11?COP??CPO ···································································· 7分 221 ?(?COP??CPO)
21 ??90??45? ··············································································· 8分
225、解（1）?装A种为x辆，装B种为y辆，装C种为10-x-y辆， ······················ 1分
? 由题意得：12x?10y?8(10?x?y)?100 ··············································· 2分 ?y?10?2x ·················································································· 3分
（2）10?x?y?10?x?(10?2x)?x ······················································ 4分
故装C种车也为 x 辆．???x≥2 ···················································· 5分
?10?2x≥2
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解得2?x?4. x为整数, ?x?2,3,4 ··················································· 6分 故车辆有3种安排方案,方案如下: