【诚心请教】关于OG12几道数学题~~ 真心感谢你的帮助

小娟子nana

Og12数学题

225. a straight pipe 1 yard in length was marked off in fourths and also in thirds. If the pipe was then cut into separate pieces at each of these markings, which of the following gives all the different lengths of the pieces, in fraction of a yard?

答案是：1/12,1/6 and 1/4

这题即使看了后面的答案和图解，也不太明白。可能主要是不明白前半句话是什么意思“a straight pipe 1 yard in length was marked off in fourths and also in thirds. If the pipe was then cut into separate pieces at each of these markings,”特别是“in fourths and also in thirds”


217 .In a certain game, a large container is filled with red, yellow, green, and blue beads worth, respectively,7 ,5,3 and2 points each. A number of beads are then removed from the container. If the product of the point values of the removed beads is 147000, how many red beads were removed?

答案是：2

这题看了后面的答案是有点明白。但主要是不太明白这个题的意思，也就是翻译。

195.a store currently charges the same price for each towel that sells. If the current price of each towel were to increased by 1dollar, 10 fewer of the towels could be bought for 120 dollar, excluding sales tax. What is the current price of each towel?

答案是：4 dollar

看了答案估计“10 fewer of the towels could be bought for 120 dollar”是省了” the unchanged price”.答案解释是设p是现在的价钱，n是可以卖掉小塔得到120dollar的台数.两个方程：（1） pn=120    （2） （p+1）（n-1）=120我的问题是，从这个题目中，怎样可以推导出方程（1）的，题目中好像没有说没变的价钱p与可以卖掉小塔得到120dollar的台数n也是120阿··

191. pat will walk from intersection x to intersection y along a route that is confined to the square grid of four streets and three avenues shown the map above. How many routes from x to y can pat take that have the minimum possible lengh?（由于不太会使用word ，画不出书上的图图，呵呵，横着的就street ，纵着的就是avenue）

如果大家看不到图，就看附件吧

答案是10

我觉得答案的方法不是很简便，一开始我是想要排列组合的方法做，但发现做不了。请问有人用了其他方法解答这题吗？


143. If [x] is the greatest integer less than of equal to x, what is the value of [-1.6]+[3.4]+[2.7]

答案是3

这题真的是看着答案解析也不明白··（我的数学阿···）


81Data for a certain biology experiment are given in the table above. If the amount of bacteria present increased by the same factor during each of the two 3-hour periods shown, how man gram of bacteria were present at 4:00p.m.

Amount of bacteria present

Time / amount
1;00pm  / 10.0grams
4;00pm / X grams
7;00pm / 14.4grams


答案是12

这题主要是不理解“If the amount of bacteria present increased by the same factor during each of the two 3-hour periods shown,”意思，特别是“the two 3-hour periods”和“increased by the same factor”。如果“increased by the same factor”是增加相同的因数的意思，为什么是相乘呢？不是相加吗？

我心向明月

143. If [x] is the greatest integer less than of equal to x, what is the value of [-1.6]+[3.4]+[2.7]

答案是3

这题真的是看着答案解析也不明白··（我的数学阿···）

如果[x]定义为小于等于x的最大整数，那么。。。

题干中是less than OR equal to X。

[-1.6] = -2，小于或等于-1.6的最大整数是多少？是-2
[3.4]=3
[2.7]=2

加一起得3。这题就是相当于定义了一个函数，然后将值代进去求具体的数值。

我心向明月

225. a straight pipe 1 yard in length was marked off in fourths and also in thirds. If the pipe was then cut into separate pieces at each of these markings, which of the following gives all the different lengths of the pieces, in fraction of a yard?

答案是：1/12,1/6 and 1/4

这题即使看了后面的答案和图解，也不太明白。可能主要是不明白前半句话是什么意思“a straight pipe 1 yard in length was marked off in fourths and also in thirds. If the pipe was then cut into separate pieces at each of these markings,”特别是“in fourths and also in thirds”

a straight pipe 1 yard in length was marked off in fourths and also in thirds
理解为：一条长为1 yard的线，被平分为3等份和4等份。

我心向明月

217 .In a certain game, a large container is filled with red, yellow, green, and blue beads worth, respectively,7 ,5,3 and2 points each. A number of beads are then removed from the container. If the product of the point values of the removed beads is 147000, how many red beads were removed?

答案是：2

这题看了后面的答案是有点明白。但主要是不太明白这个题的意思，也就是翻译。

--------------

在一游戏中，向一个大的容器中装红，黄，绿、蓝beads worth，分别是7,5,3,2点（即：红7，黄5，绿3，蓝2）。将一定数量的beads从容器中拿出。如果拿出的点数乘积（product）是147000，多少红色的bead被拿出？

我心向明月

191. pat will walk from intersection x to intersection y along a route that is confined to the square grid of four streets and three avenues shown the map above. How many routes from x to y can pat take that have the minimum possible lengh?（由于不太会使用word ，画不出书上的图图，呵呵，横着的就street ，纵着的就是avenue）

如果大家看不到图，就看附件吧

答案是10

我觉得答案的方法不是很简便，一开始我是想要排列组合的方法做，但发现做不了。请问有人用了其他方法解答这题吗？

这题应该是有一个比较的简单的解法，不过，没有想出来。

我心向明月

195.a store currently charges the same price for each towel that sells. If the current price of each towel were to increased by 1 dollar, 10 fewer of the towels could be bought for 120 dollar, excluding sales tax. What is the current price of each towel?

答案是：4 dollar

看了答案估计“10 fewer of the towels could be bought for 120 dollar”是省了” the unchanged price”.答案解释是设p是现在的价钱，n是可以卖掉小塔得到120 dollar的台数.两个方程：（1） pn=120    （2）（p+1）（n-1）=120我的问题是，从这个题目中，怎样可以推导出方程（1）的，题目中好像没有说没变的价钱p与可以卖掉小塔得到 120 dollar的台数n也是120阿··

-----------------------

OG解释中的假设：p是原价，n是原价情况下，120元可以买的毛巾数量；

那么：

p+1是现价，
n-10是现价情况下，120能买的毛巾数量

小娟子nana

我感觉是用排列组合的方法做的，但想不到怎么做···

小娟子nana

有谁会81题阿？？

我心向明月

忘记了一道，抱歉：

81. Data for a certain biology experiment are given in the table above. If the amount of bacteria present increased by the same factor during each of the two 3-hour periods shown, how many gram of bacteria were present at 4:00p.m.

Amount of bacteria present

Time / amount
1;00pm  / 10.0grams
4;00pm / X grams
7;00pm / 14.4grams


这题主要是不理解“If the amount of bacteria present increased by the same factor during each of the two 3-hour periods shown,”意思，特别是“the two 3-hour periods”和“increased by the same factor”。如果“increased by the same factor”是增加相同的因数的意思，为什么是相乘呢？不是相加吗？

---------------------

factor: 因子，涉及到factor，不可能是加的。

(x-10)/10=(14.4-x)/x

x^2-10x=144-10x
x=12

小娟子nana

那“the two 3-hour periods”是什么意思阿？谢谢哦~~~~回答得很详细~