Julia spent $58 on a book. the cost of the book was $20 less than twice what she spent on a backpack. how much did the backpack cost?

Identify all the cases where probability sampling is used. selecting the first 100 students who enter a school during the day selecting every 100th package to be reviewed for its contents surveying every member of a city of 100,000 people dividing fans into groups of 100 and ask 10 people from each group selecting 100 social media friends to answer a survey selecting 100 numbers at random from a group of 100,000