Manhattan free test 数学34题

dongweiyao · 发表于 2015-12-27 12:02:22

[size=12.0012px]90 students represent x percent of the boys at Jones Elementary School. If the boys at Jones Elementary make up 40% of the total school population of x students, what is x?

[size=12.0012px]

		125
		150
		225
		250
		500

[size=12.0012px]正确答案是150. 小弟看不懂这个题目什么意思啊，特别是第一句话。灰色部分为Manhattan的解析，还是晕，求解啊！

[size=12.0012px]解析：[size=12.0012px]We are told that the boys of Jones Elementary make up 40% of the total of x students.[size=12.0012px]

Therefore: # of boys = .4x

We are also told that x% of the # of boys is 90.
Thus, using x/100 as x%:
(x/100) × (# of boys) = 90

Substituting for # of boys from the first equation, we get:
(x/100) × .4x = 90
(.4x2) / 100 = 90
.4x2 = 9,000
x2 = 22,500
x = 150

叫我西瓜 · 发表于 2015-12-27 20:07:21

90=x%*boys=x%*40%*x
90 students represent x percent of the boys at Jones Elementary School. If the boys at Jones Elementary make up 40% of the total school population of x students

木子笛子 · 发表于 2015-12-27 21:13:25

90=x%*男
0.4X=男通过男建立等式
所以90/x%=0.4x
x=150

Manhattan free test 数学34题

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