.......or if you don't have a planet brain like the previous posters or you are in the air, here are some ballpark figures (assuming ISA)
SL 660kts (+15C)
FL250 600kts (-35C)
FL360 570kts (-56C)
Add 1kt/degree above ISA: subtract 1kt,degree blw ISA (appx)
M.78 TAS in ISA (-56C) 447kts
0.01M = 6kts TAS (appx)
From these, you can work out/verify most things (approximately) if you need to.
With apologies to the clever!!
mcdhu