The results of surveying 100 residents of a city reported that 40 read the daily morning paper, 70 read the daily evening paper & 20 read neither. how many: .1. read at least 1 paper? 2. read both? 3. read exactly one daily paper?

From the data given, we can obtain the number of people reading at least 1 paper by taking the difference between the universal set and the set containing people not reading anything. The answer in 1 is 100-20 equal to 80. In 2, the answer is 40 + 70 - 80 equal to 30 people. 3. The people reading exactly one daily paper is 50 people

(40 - x) + (70 - x) + x + 20 = 100
130 - x = 100
-x  = 100 - 130
-x = -30
x = 30

read daily morning paper = 10
read the daily evening paper = 40
read both papers = 30
read neither paper = 20

how many read at least one paper : 80
read both = 30
read exactly one = 50

C. expression because any expression or equation may contain more than one variable