【解答】解:BC+AD=(60×2)÷6=20(cm)…①, BC﹣AD=4cm…②, 由①②,可得
BC=12(cm),AD=8cm;
因为三角形ACD的面积等于AC乘以CF,再除以2, 所以三角形ACD的面积等于长方形ACFE的面积的一半, 因此阴影部分的面积等于三角形ACD的面积,
则阴影部分的面积=AD×CD÷2=8×6÷2=24(cm). 答:阴影部分的面积是24cm.
29.(10分)成都青年旅行社“五一”推出甲、乙两种优惠方案: 甲:成都一日游,大人每位全票80元,小朋友四折 乙:成都一日游,团体5人以上(含5人)每位六折 (1)李老师带5名小朋友游览,选哪种方案省钱? (2)李老师和王老师带4名小朋友游览,选哪种方案省钱?
(3)张三、王五两位小朋友及各自的父母6人游览,选哪种方案省钱?
【解答】解:甲方案票价:大人每位全票80元,小朋友四折为80×0.4=32(元) 乙方案票价:团体5人以上(含5人)每位六折80×0.6=48(元) (1)李老师带5名小朋友游览 甲方案:1×80+80×0.4×5=240(元) 乙方案:(1+5)×(80×0.6)=288(元) 240<288
答:李老师带5名小朋友游览,选甲方案省钱. (2)李老师和王老师带4名小朋友游览 甲方案:2×80+80×0.4×4=288(元) 乙方案:(2+4)×(80×0.6)=288(元) 288=288
答:李老师带5名小朋友游览,选甲乙方案都可以. (3)张三、王五两位小朋友及各自的父母6人游览 甲方案:4×80+80×0.4×2=384(元) 乙方案:6×(80×0.6)=288(元)
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2
2
384>288
答:张三、王五两位小朋友及各自的父母6人游览,选乙方案省钱. 30.(10分)系统找不到该试题
31.(10分)环绕小山一周的公路长1920米,甲、乙两人沿公路竞走,两人同时同地出发,反方向行走,甲比乙走得快,12分钟后两人相遇.如果两人每分钟多走16米,则相遇地点与前次相差20米.
(1)求甲乙两人原来的行走速度.
(2)如果甲、乙两人各以原速度同时同地出发,同向行走,则甲在何处第二次追上乙? 【解答】解:(1)甲乙原来的速度之和是:1920÷12=160(米), 提高速度之后的速度之和是:160+16+16=192(米),
所以提高速度之后二人相遇的时间是:1920÷192=10(分钟),
设甲原来的速度是x米/分,则提高速度后,甲的速度是(x+16)米/分,根据题意可得方程: 12x﹣10(x+16)=20, 12x﹣10x﹣160=20, 2x=180, x=90,
则乙原来的速度是:160﹣90=70(米/分),
答:甲原来的速度是90米/分,乙原来的速度是70米/分;
(2)1920×2÷(90﹣70) =1920×2÷20 =192(分),
192×90÷1920=9,说明正好在出发点. 答:甲在出发点第二次追上乙.
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