There are only four single-digit primes: 2, 3, 5, and 7. So all two-digit numbers are either prime, or divisible by one of these four numbers. Of the four, 2, 3 and 5 are all very easy to spot check whether a number is divisible by them or not (for 3, add the digits first, and see if that sum is divisible by 3). If a given 2-digit number doesn’t fall into this category, 7 times out of 8, it’s prime. ...
I love pomodoros 🍅. But I have to admit, most of the time when I reach for them, it’s because I"m already having trouble staying on task with whatever I’m doing. I generally don’t get a lot of value out of the ’longer break’ option, a steady beat of work and breaks is enough for me. In those circumstances I often find solace in the idea that a well-constructed pomodoro creates a certain lower bound on my work-to-play leverage ratio. The classic 25 minutes on, 5 minutes off gives you a 5:1 ratio. ...
A communication heuristic, optimized for asynchronous communication of detailed concepts between human beings. Not really a TIL, I’ve been sitting on this one for a while. Rationale Existence “proof” Our short term memory can hold at best about 7 +/- 2 chunks of information at a time. Start with the lower end of that: 5 chunks. Assume that whatever someone is “really” trying to do takes up 1 of those 5. We’re left with 4 chunks. Conclusion Organize your work processes as much as possible so that they can be effectively understood using at most 4 chunks of short-term memory. If you feel a process is too complicated to be held like that, find conceptual fault lines to hack against until it’s true. ...