> What if I have a recipe for three servings but five dinner guests? Doubling is a useful skill, sure. > If I just passed milepost 472 and I average 55 miles

> What if I have a recipe for three servings but five dinner guests? Doubling is a useful skill, sure. > If I just passed milepost 472 and I average 55 miles per hour, how long will it take me to reach Mexico? This would never come up, because my phone navigation will tell me at any point along the trip how long it will take, more accurately because it has my full speed data plus knowledge about traffic and other hazards ahead. > How many bottled liters of water can I fit in this box? Unless I have another box under consideration, then I probably intend to fit as many as possible, so I'll just fill. Complicating this problem can make a need to calculate (or count) more apparent, but further complications can also make a need to compute with a program more apparent too. > How much is the 1.35% annual property tax on a million-dollar house, per month? About 1e6/1e2/1e1, or $1000. If I want to be more accurate then I would use a computer -- 1. because I'm likely at my computer already when this comes up, 2. because if not I still likely have a phone. Both you and chongli ought to consider this argument (ignore the stuff about violent video games): https://theodoregray.com/BrainRot/ https://theodoregray.com/BrainRot/