Final answer:
The fifteen-year-old might overestimate the number of guests by assuming all invitees come and bring extra friends, and underestimate snacks by planning for just one snack per guest, not considering seconds or differing appetites.
Step-by-step explanation:
A fifteen-year-old hosting a birthday party at a swimming pool might need to make several estimates for party preparations. Two types of estimates are to be considered here, one likely to be an overestimate and the other likely to be an underestimate.
Option 1: Estimate of the Number of Guests Attending
An overestimate may occur if the fifteen-year-old assumes that all invited guests will come and brings extra friends, resulting in a higher count than the actual. For example, if 20 guests were invited and she estimates that each would bring a friend, this would yield an estimate of 40 attendees.
Option 2: Estimate of Snacks Needed for the Party
An underestimate might happen if the fifteen-year-old plans for fewer snacks than what may actually be needed. This could occur if she accounts only for one snack per guest, not considering that guests may desire seconds or have different appetites.