GWD31-9 三道数学不解~~！求助~~~~

toneere

Q9
In the xy-plane, if line k passes through the points
(3.-4) and (a,b), where b=4a-16 and a≠3,
what is the slope of k?
A.    –4
B.    –1/2
C.    0
D.    2
E.    4

Q23.
At a fruit stand yesterday, the price of each apple was $0.10 more than the price of each orange. What was the total revenue from the sale of oranges at the fruit stand yesterday?
(1) The number of oranges sold at the fruit stand
  yesterday was 5 more than the number of
  apples.
(2) The total revenue from the sale of apples
  at the fruit stand yesterday was $15.00

Q32.
Last year in a group of 30 businesses, 21 reported a net profit and
15 had investments in foreign markets. How many of the businesses
did not report a net profit nor invest in foreign markets last year?
(1) last year 12 of the 30 businesses
  reported a net profit and had invest-
  ments in foreign markets.
(2) last year 24 of the 30 businesses
  reported a net profit or invested in
foreign markets, or both.

sererse

Q9,其实就是问直线b=4a-16(也就是y=4x-16)的斜率，注意（3，-4）本身就在这条直线上。可以这样理解，点（a,b)是动点，移动的轨迹是b=4a-16

yayajiaojiao

Q23， 设苹果价钱为a， 桔子为o, 昨天卖了A个苹果，O个桔子， 已知a-o=0.1, 求O*o
如果知道1， O=A+5， O*o=oA+5o， 可是我们只知道a和o的关系，所以1自己不能求出O*o.
如果知道2， A*a=15， 我们同样求不出O*o。
如果知道1和2， A*a=(O-5)*(0.1+o)=O*o-0.5+0.1O-5o.=15，貌似我们还是求不出O*o。
现在要考虑A和O是整数会不会影响方程的解， 如果A=1， a=15, o=15.1, O=6, 貌似O*o虽然夸张但是也可以。如果A=2, a=7.5, o=7.4, O=7, O*o也没什么不行。

所以我认为1+2也不行，不知道对不对

yayajiaojiao

Q32 设只投资海外没有盈利的为I,只盈利没有投资海外的为P，两个都有的为X,两个都没有为Y。
那么P+I+X+Y=30， P+X=21, X+I=15， 求Y

如果知道1， X=12， 可知I=3, P=9, Y=6
如果知道2，I+P+X=24， 所以Y=6
所以2个条件都可以