The classic version is: Wind / (TAS/60). My top tip is that obviously TAS/60 = nms/min. So I just round that to 1, 1.5, 2, 2.5, etc for cardinal TAS speeds of 60, 90, 120, 150, etc. Much easier to to the mental stuff when the pressure is on like that. The nms/min number pops up in many rules of thumbs. Although in this case you would normally figure it out on the ground.
say W/V 280/24 What would be the max drift? and how did you work it out?
As mentioned above, you need the TAS to do the sum.