In a survey of computer owners, 80% use an anti-virus program, 25% use an anti-spyware program and 15% use both. what is P(anti-spyware I anti-virus)?

A circle is 360° all the way around; therefore, if you divide anarc's degree measure by 360°, you find the fraction of the circle's circumference that the arc makes up. Then, if you multiply the length all the way around the circle (the circle's circumference) by that fraction, you get the length along thearc.