GWD-6-28
Last Sunday a certain store sold copies of Newspaper A for $1.00 each and copies of Newspaper B for $1.25 each, and the store sold no other newspapers that day. If r percent of the store’s revenues from newspaper sales was from Newspaper A and if p percent of the newspapers that the store sold were copies of newspaper A, which of the following expresses r in terms of p?
A. 100p / (125 - p)
B. 150p / (250 - p)
C. 300p / (375 - p)
D. 400p / (500 - p)
E. 500p / (625 - p)
A/(A+B)=P/100
A/(A+1.25B)=r/100
其中A,B是卖掉的报纸份数(copies)
A卖了X，B卖了Y
(1X+1.25Y)×r%=1X
(X+Y)×p%=X
两个联立得出400p / (500 - p)
(p/100*1.00)/[p/100*1.00+(100-p)/100*1.25]=r/100
[以上是GWD-6-28题网上讨论的内容。式子我明白(1X+1.25Y)×r%=1X
(X+Y)×p%=X
但是，不知道如何带入才能得出答案D。请大家明白的NN们指点一下。]
补充题-ps-Section 1-5
At a certain diner, a hamburger and coleslaw cost $3.59, and a hamburger and french fries cost $4.40. If french fries cost twice as much as coleslaw, how much do french fries cost?
(A) $0.30
(B) $0.45
(C) $0.60
(D) $0.75
(E) $0.90
[我列的式子是：H+C=3.59; H+F=4.40; F=2C 就是算不出0.9，哪位帮助指点一下我的式子哪里错了？]
补充题-ps-Section 1-19
Month Average Price per Dozen
April May June $1.26 $1.20 $1.08
19. The table above shows the average (arithmetic mean) price per dozen of the large grade A eggs sold in a certain store during three successive months. If as many dozen were sold in April as in May, and twice as many were sold in June as in April, what was the average price per dozen of the eggs sold over the three-month period?
(A) $1.08
(B) $1.10
(C) $1.14
(D) $1.16
(E) $1.18
[这题不知道是不是也因我列的式子有问题，总之就是算不出和答案一样的结果。我是这样列的式子：分别设销售的数量为：A;M;J
2/3*A=M; A=2*J; 然后列式子：分子为1.26*A+1.20*M+1.08*J; 分母为：A+M+J 再带入
请帮忙指点一下错误。]
补充题-ps-Section 2-12
12. A bus trip of 450 miles would have taken 1 hour less if the average speed S for the trip had been greater by 5 miles per hour. What was the average speed S, in miles per hour, for the trip?
(A) 10
(B) 40
(C) 45
(D) 50
(E) 55
[请教这题如何理解great by？这里的意思是不是说：如果速度增加5英里每小时，行450里就少用1小时？哪位帮忙列一下式子？我实在算不出答案。]
补充题-ps-Section 3-16
16. A family made a down payment of $75 and borrowed the balance on a set of encyclopedias that cost $400. The balance with interest was paid in 23 monthly payments of $16 each and a final payment of $9. The amount of interest paid was what percent of the amount borrowed?
(A) 6%
(B) 12%
(C) 14%
(D) 16%
(E) 20%
[这题我不明白题目的意思，请求帮助指教]
补充题-ps-Section 3-17
17. If x≠0 and , then, in terms of y,
(A) 2y
(B) y
(C)
(D)
(E) -2y
[这题我完全不知道从何入手，请求指教] | 
