A computer company advertises its computers in PC World, in PC Magazine, and on television. A survey of 770 customers finds that the numbers of customers who are familiar with the company’s computers because of the different forms of advertising are as follows. 305, PC World, 290, PC Magazine, 390, television, 110, PC World and PC Magazine, 135, PC Magazine and television, 150, PC World and television, 85, all three sources. How many of the surveyed customers know about the computers because of a. exactly one of these forms of advertising?
b. exactly two of these forms of advertising?
c. PC World magazine and neither of the other two forms of advertising?