What is the probability you pick a student in the school and they prefer to use Tik-Tok OR they are a Junior? (Write as a percent rounded to the nearest hundredth)

Question

Tik-Tok Snapchat Total

Freshman 345 122 467

Sophomore 289 203 492

Junior 178 109 287

Senior 103 189 292

Total 915 628 1538

Answer 1

P(prefer tiktok or a junior) = P(prefer tiktok) + P(junior) - P(tiktok and junior)

= 915/1538 + 287/1538 - 178/1539 = (915 + 287 - 178)/1538 = 1024/1538 = 0.6658 = 66.58%.