几道OG中PS的题，79、116、124、127、129、138

紫色的月亮

这几题是我做错的题,对了对答案,可是不知道正确答案是怎么解出来的.有人能帮忙解答一下么,谢谢! OG PS里的题:

79. R is the set of positive odd inntegers less than 50, and S is the set of the squares of the integers in R. How many elements does the intersection of R and S contain?

(A)None   (B)Two  (C)Four  (D) Five  (E) Seven  我选的B, 正确答案是C

 

116. Each "." in the milage table above represnets and entry indicating the distance between a pair of the five cities. If the table were extended to represent the distances between all pairs of 30 cities and each distance were to be represented by only one entry, how many entries would the table then have?

(A)60  (B)435  (C)450  (D)465  (E)900

 

124. According to a car dealer's sales report, 1/3 of the car sold during a certain perild were sedans and 1/5 of the other cars sold were station wagons. If N station Wagons were sold during that period, how many sedans, in terms of N, were sold?

(A) 2N/15   (B)3N/5  (C)5N/3  (D)5N/2  (E)15N/2  

 

127. To mail a package, the rate is X cents for the first pound and y cents for each addtional pound, where x>y. Two packages weighting 3 pounds and 5 pounds, respectively, can be mailed separately or combined as one package. Which method is cheaper, and how much money is saved?

(A)Combined, with a saving of x-y cents

(B)Combined, with a saving of y-x cents

(C)Combined, with a saving of x cents

(D)Separately, with a saving of x-y cents

(E)Separately, with a saving of y cents

我选的是E, 正确答案是A...

 

129. On a recent trip, Cindy drove her car 290  miles, rounded to the nearest 10 miles, and used 12 gallons of gasoline, rounded to the nearest gallon. The actual number of miles per gallon that Cindy's car got on this trip must have been between:

(A) 290/12.5 and 290/11.5

(B)295/12 and 285/11.5

(C) 285/12 and 295/12

(D) 285/12.5 and 295/11.5

(E) 295/12.5 and 285/11.5

这题我有点反应不过来了,晕...

 

138. At a loading dock, each worker on the night crew loaded 3/4 as many boxes as each worker on teh day crew. If the night crew has 4/5 as many workers as the day crew, what fraction of all the boxes loaded by the two crews did the day crew load?

(A)1/2

(B)2/5

(C)3/5

(D)4/5

(E)5/8

 

ssl507

79． 1  9  25  49 不是刚好四个吗，你忘记算上1了吧。

116. C（30，2）=435

124. Sedans: station wagons=1/3:1/5*2/3=5:2

So. Answer D, 看清1/5 of the other

127. x>y，so combined is cheaper. 这题简单，再看一遍题目吧！ 

 129．
            Between, 就是算最大值和最小值，最大值肯定是分子最大(29.5)，分母最小的时候  (11.5)，最小值刚好相反(分子28.5，分母12.5)。所以D

138．Crew load的boxed总量=每个工人的load量*工人数。

So, night crew load的boxed总量：day crew load的boxed总量=3/4*4/5:1=3/5:1

So, day crew load的比例=1/(1+3/5)=5/8

btw，og不是有答案解释吗?

紫色的月亮

OG有答案解释么?我的没有呀.我是从CD下载的OG11,有答案,但是没有答案解释...

紫色的月亮

谢谢你的解答,我现在搞懂这些题了.