Re: [計量] 幾題想請問一下
※ 引述《leslielion ()》之銘言：
: 1.
: A store currently charges the same price for each towel that it sells. If the
: current price of each towel were to be increased by $1, 10 fewer of the
: towels could be bought for $120, excluding sales tax. What is the current
: price of each towel?
: Ans. $3
: 我從網路上找的解答:
: current price-x
: current quantity-y
: x*y=120
: current price increased by 1 =(x+1)
: current quantity decreased by 10=(y-10)
: (x+1)*(y-10)=120
: solving two equations
: x^2+x-12=0
: x=3
: 但我困惑的是，我從文意中讀不出x*y=120這一項，然後來跟(x+1)(y-10)=120來解聯立
: 由原題我只能了解(x+1)*(y-10)=120這一項而已。
: 2.
: The ratio, by volume, of soap to alcohol to water in a certain solution is
: 2:50:100. The solution will be altered so that the ratio of soap to alcohol
: is doubled while the ratio of soap to water is halved.
: If the altered solution will contain 100 cubic centimeters of alcohol, how
: many cubic centimeters of water will it contain?
: Ans. 800
: 這題我不懂的是，為什麼
: "ratio of soap to water is 2:100 if it is halved it us 4:400"(網路上找的解答)
: ?
肥皂:酒精: 水
2: 50 :100
肥皂:酒精濃度變成原來的兩倍，則肥皂濃度乘以2
肥皂:酒精: 水
4 : 50 :100
肥皂:水濃度變成原來的一半，則2:100變成1:100=4:400則
肥皂:酒精: 水
4 : 50 :400
現在酒精有100毫升，根據以上比例
水有 800 毫升
: 3.
: The arithmetic mean and standard deviation of a certain normal distribution
: are 13.5 and 1.5, respectively. What value is exactly 2 standard deviations
: less than the mean?
: Ans. 10.5
算術平均數是13.5，標準差是1.5，請問算術平均數以下兩個標準差的值是多少？
13.5-(1.5*2)=13.5-3 =10.5
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※ 編輯: oogu 來自: 61.228.241.146 (10/01 23:38)
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