[問題] GWD6-Q28

[kwtluck]

Q28:
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?

100p / (125 - p)
150p / (250 - p)
300p / (375 - p)
400p / (500 - p)
500p / (625 - p)

Answer: D =>麻煩各為大大解惑Thanks!!~~

[kwtluck]

石沉大海~~SOS

[lance921]

A 賣出p percent 表示 B賣出 1-p percent
1*p 賣出A的所得 1.25*(1-p)賣出B的所得
(1*p+1.25*(1-p)) 就是全部所得
r = 1*p /(1*p+1.25*(1-p))
算一算就求出D拉

[kwtluck]

**感謝lance921大大的指導**
Thanks!!~~

[chris8888]

對, 但這樣不夠完整 :

1. 先假設全部的銷售量是a份報紙

2. Newspaper A revenue : p * a * 1
Nespaper B revenue : (1-p) * a * 1.25

3. r = (pa) / (pa + 1.25a(1-p)) => a通通去掉 => 經過簡化約分變成 p / (1.25-0.25p) => 全部成以400 => 400p / (500-p)

[chencraig0227]

對, 但這樣不夠完整 :

1. 先假設全部的銷售量是a份報紙

2. Newspaper A revenue : p * a * 1
Nespaper B revenue : (1-p) * a * 1.25

3. r = (pa) / (pa + 1.25a(1-p)) => a通通去掉 => 經過簡化約分變成 p / (1.25-0.25p) => 全部成以400 => 400p / (500-p)

上述反藍部分算出來也不是答案

要很小心的是
這裡的P跟R 單位都是percent
所以運算的時候 要把 P變成P/100 ; R變成 R/100這樣才算的出答案!