公务员考试网 发表于 2017-4-6 09:51:07

数量关系答题技巧之多法并用巧练题

很有考友都曾提到:我做了很多题,但提升效果有限。实则并不然,一般来说,只要你是认真做的,就肯定有提升,但提升是一个渐变的过程,并不明显。那么,怎样才能提升做题的效率呢?答案很简单,多开发你大脑,让它转起来。比如说你做一道题,多想想不同的解法,锻炼不同的解题思维,不再受定势思维的局限,多转动你的思维,运用最恰当的方法解题,通过不断地锻炼,逐渐将各种技巧变为自己所用。
例1、某单位共有A.B.C.三个部门,三部门人员平均年龄分别为38岁,24岁,42岁,A和B两部门人员平均年龄为30岁,B和C两部门人员平均年龄为34岁,该单位全体人员的平均年龄为多少岁?( )
A 34
B 36
C 35
D 37
解析:
解法一:方程法。设A部门x人,B部门y人, C部门z人,则38x+24y=30(x+y),求得x/y=3/4,x=0.75y;24y+42z=34(y+z)求得z/y=5 /4,z=1.25y,可以知道部门总人数为y + 0.75y+1.25y=3y,平均年龄=(38×0.75y + 24y + 42×1.25y)÷3y=35岁。故答案为C。
解法二:题干跟浓度问题的混合溶液很类似,因此,可考虑用十字交叉法。依题可得:
http://www.zzxingce.com/xingce/datijiqiao/shuliangguanxi/20140214/data:image/png;base64,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
http://www.zzxingce.com/xingce/datijiqiao/shuliangguanxi/20140214/data:image/png;base64,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
所以A、B部门的人数之比为6:8=3:4;B、C部门的人数之比为8:10=4:5,根据比值可假设三个部门的人数分别为3、4、5,则平均年龄=(38*3+24*4+42*5)÷(3+4+5),可利用尾数法快速求解(被除数的尾数是0,除数的尾数是2,那么,商的尾数只能是5),只有C符合,故答案为C。
       
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