Think of those occasions where you are moving house. You know that the volume of items you need to shift is enough to fill about twenty identical boxes – except that it would require far too much time and planning to work out what to put where. Instead, you go for the easiest method of packing, which is to put items at random into the first box, and, when the next item you pick up doesn’t fit, you seal up the box you have been filling and start on a new one. This is known as a ‘first-fit strategy’. How efficient is it? It turns out that, however unlucky you are with the order in which things come to hand, the number of boxes you need will always be within 70 per cent of what could be achieved with perfect allocation. So if your best possible is 20 boxes, you can reassure yourself that even the lazy first-fit method strategy should require at most 34 boxes. If this isn’t good enough – and, let’s be honest, 70 per cent is a bit of a waste, though this is the worst-case scenario – a strategy of packing the biggest things first and the smallest last always turns out to be within 22 per cent of the very best solution. This means a worst case of 25 boxes, instead of the optimal 20. And, since many of us tend to use a biggest-first strategy, especially when filling the car boot, this shows that when it comes to packing, common sense is a good substitute for deep mathematical thinking. […]

[T]he building needs thirty floors just to enable the lift to reach top speed for a few moments. And that’s assuming that the lift gets a clear run. In a busy building, a lift is likely to make lots of short trips, which means it will rarely have a chance to accelerate to high speed. Added to this, the time saved in speeding up the lift will be small compared with the time spent opening and closing the doors to let passengers in and out. In other words, making the lifts go faster has little impact on the overall waiting time.[…]

For example, imagine you are three floors down in the basement of a building with two lifts. The indicator tells you that there are lifts sitting on higher floors, one on the ground floor and one on the third floor. You call the lift, and notice that the one that comes to collect you is the one from the third floor – despite being twice as far away. Why didn’t the ground-floor lift come to you? The answer is that ‘intelligent’ lifts are often programmed to have a slight bias towards sticking to the ground floor, where most of the passengers get on. The intelligent lift may calculate that it’s worth sending a more remote lift to collect you if it means that it can keep a lift waiting at the ground floor, where a flurry of passengers could arrive at any moment. You are being sacrificed (modestly) for the greater good. Here is another possible sacrifice. An intelligent lift is seeking to keep down both the average and the maximum waiting time. A customer on Floor 6 calls a lift, but is dismayed when it bypasses them to collect somebody at Floor 9. The reason might be that the modern intelligent lift is aware that the Floor 9 person has already been waiting for a minute and is therefore top priority. With this urgent case on Floor 9, the lift reckons that you on Floor 6 can wait a few more seconds. […]

In fact the Black Death entered Europe when a Tartar army catapulted infected corpses into a Genoese trading post […]. […]