SAT数学Problem Solving练习题（13）

>>SAT考试：SAT数学Problem Solving练习题（13）

>>SAT考试辅导：精品课程高端指导

Question 13: Out of 25 mining companies, 14 extract copper, 16 extract silver and 1 extracts neither copper nor silver. How many companies extract both silver and copper?

(a) 1

(b) 6

(c) 2

(d) 15

(e) 3

Answer: If x is the number of companies that extract both metals,

1. the number of companies that extract copper only is 14 - x;

2. the number of companies that extract silver only is 16 - x;

There are 4 types of companies:

-that extract copper only,

-silver only,

-both copper and silver

-neither copper nor silver.

Their total should be 25:

25= 14 - x + 16 - x + x + 1

x = 31 - 25 = 6

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