Earlier I wrote about remembering fractions of 6 due to influence of cricket. In the footnotes there, I mentioned also being good with number 7.
I remembered why I (subconsciously) know so many multiples and fractions of 7. It’s got to do with all those physics problems in high school.
Gravitational acceleration (g) near earth is 9.8m/s2. This can also be written as 7*7*2/10.
2 and 10 are easy to manoeuvre. 7 required me to calculate the fractions and multiples.
Since there were a lot of questions with g involved, I subconsciously memorised the frequent multiples and fractions. Now, decades later, I still (subconsciously) remember a fair number of them without having to bother with the calculation.
The weird bit about most of these values is that I don’t usually know them till I need them. When confronted by the need to calculate such a fraction or multiple, the answer will just start ringing in my head before I’ve calculated it. The trouble with this is that sometimes I’ll still work the value out just to be sure that the memory is serving the correct answer.