This one might sound simple to everyone, but I am the worlds worst at mental math.
What was killing me was diversions, where my instructor would ask how long it will take. Speed for the leg, 87kts distance 18nm. I would tie my head in knots trying to figure it. Somebody told me a much easier way to think of it.
Divide the speed by 10, so this gives the distance covered every 6 mins, i.e. 8.7 nm. I find this way I can then put this into distance, i.e. approx 12mins.
I'm sure many of you are looking at this and going "yeah, thats obvious!" but I found working out the times and speed in my head tricky when asked and also flying and navigating a diversion. If one person says "thats quite helpful" then I will have fulfilled the purpose of this post!