Determine whether the situation requires an exact calculation or an estimate. Explain.
This week, the Laketown Cruise Company took its boat on 19 cruises, carrying the boat's full capacity of 38 guests on each cruise. Was this week's total guest count smaller than last week's count of 765?
I would think exact calculation would be vital, considering these are lives, but is that a reason for mathematics?
I think the answer expected is "exact", but for a different reason. (Unless somebody went missing, or the food was contaminated!)
An estimate is going to be high, and you know it will be high: 20 * 40. A closer estimate 20 * 40 - 40 will be low, but close, and what you want to know is whether the numbers are up or down.
If somebody just asked "how many last week?", then "a bit under 800", or "around 760" would do, or if there were 1000 last week, then we'd know it could be down, and an estimate would do.
My opinion: exact. But it's just opinion.