Chapter 6 - Percent - 6.4 Using Proportions to Solve Percent Problems - 6.4 Exercises - Page 420: 51

$$85\text{%}$$

We see that 15 percent of American youth use Tumblr as part of their social media. Thus, the percent of Americans who do not use Tumblr as part of their social media is: $$ =100\text{%}-15\text{%} \\ =85\text{%}$$