Question

A blogger who is just starting out made three videos. So far, she has 312 subscribers, who watched one, two, or all three videos. The three videos got 740 total views all together. Assuming each subscriber only viewed a particular video once, how many more people watched all three videos than only one video?

Answer 1

116. Suppose x subscribers watched only one video, y watched two, and (312-x-y) watched three. There are 740 views in total, so x+2y+3(312-x-y)=740. -2x-y=-196, or 2x+y=196. The number of people who watched three videos is 312-x-y=312-(2x+y)+x=312-196+x=116+x. 116+x-x=116.