请求高人帮助,这个小六数学题如何解答?

2013-06-17 · 1805 阅读
本帖最后由 那时烟花 于 17-6-2013 12:33 编辑

The average number of sit-ups performed by 15 girls and some boys was 50.
The average number of sit-ups performed by the girls was 80% of the average number of sit-ups performed by all the pupils.
The average number of sit-ups performed by the boys was 30% more than the average number of sit-ups performed by the girls.
(a). What was the average number of sit-ups performed by the girls?
(b). What percentage of the pupils were boys?

Answer:

(a). 50 X 80% = 40

(b). ???

请教高人解答(b), 谢谢。
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回答|共 4 个

yuebaby LV13

发表于 17-6-2013 14:29:30 | 显示全部楼层

小狮租房
不知道做的对不对.

The average number of sit-ups performed by the boys was 30% more than the average number of sit-ups performed by the girls.

so average number of st-ups is 30%*40 + 40=52
if the average of 15 girls change from 50 to 40, means  the total number of sit-ups boys performed is more than that of girls (50-40)*15=150,  one boy is only more than 2 sit-ups, so 150/(52-50)=75, the total number of boy is  75

75/(75+15)*%=83%

republic LV9

发表于 17-6-2013 17:29:22 | 显示全部楼层

40%

txwd LV8

发表于 19-6-2013 14:16:35 来自手机 | 显示全部楼层

不是吧,这就是个简单的代数题!!就是个x,y嘛。六年级题和国内4,5年级的一样。


lianlian.z LV6

发表于 7-7-2013 14:58:04 | 显示全部楼层

原题:
The average number of sit-ups performed by 15 girls and some boys was 50.
The average number of sit-ups performed by the girls was 80% of the average number of sit-ups performed by all the pupils.
The average number of sit-ups performed by the boys was 30% more than the average number of sit-ups performed by the girls.
(a). What was the average number of sit-ups performed by the girls?
(b). What percentage of the pupils were boys?


英文红色部分是解答,中文即括号里的部分辅助说明一下 =)

a) 50 X 80% = 40 sit-ups (平均每个女生)

b)  The average number of sit-ups performed by the boys was 30% more than the average number of sit-ups performed by the girls.
    100%+30%=130% (the average number of sit-ups performed by the boys was 130% of that performed by the girls)
    40x130%=52 sit-ups (平均每个男生)
    52-50=2 sit-ups    (平均每个男生比总平均多做两个)
    50-40=10 sit-ups  (平均每个女生比总平均少做十个)
    (换言之,每个女生少于总平均的部分需要五个男生来持平)
    可以直接写   No. of boys : No. of girls = 10 : 2 = 5: 1 (第一,男生女生数量比例和男生女生同总平均值差出的量成反比; 第二,提醒孩子化比例为最简)
What percentage of the pupils were boys?
   5 / (5+1)x 100% = 83 1/3 % (由于电脑不能输入除号,用 '/' 代替,家长解释的时候提醒孩子)
    同时 数学答案,即使是关于百分比的,也不可四舍五入,有需要的情况下,需用分数表示,如此题)


很多学校不要求写单位 但是个人建议孩子养成好习惯 因为将来判卷老师不一定不介意孩子忽略单位 或者缺少步骤 没必要让孩子冒险吃亏
写出每一个步骤  说明孩子条例清晰 王家长解释时 提醒孩子

=)
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