How to quickly work out the head and tail wind component in your head

An easy way to work out cross wind and head wind component is using this simple mathematical formula.
For calculating cross wind. If the wind it 30 degrees off the nose it is .5 the wind strength, 45 degrees off .7 the wind strength, 60 degrees off it is .9 the wind strength, and if 90 degrees of then obviously it is full strength. This applies on cross country flights, or for working out the cross wind when coming in to land.
If for example when coming in to land the wind is 60 degrees off the runway heading it is .9 times the wind strength, so using simple arithmetic on a 20 knot wind just multiply 9 by 2 which is 18 knots.   For a wind of 30 knots and 45 degrees off the runway heading the calculation is 3 X 7 which is 21 cross wind component.  If like me you learned your multiplication tables as a child, this is easy.
If you reverse the formula, you can use it to work out head wind or tail wind component as well.  So if the wind is directly towards you, it is full strength, if 30 degrees off it is .9 of full strength, 45 degrees off .7 of full strength, and 60 degrees off it will be half strength.
If it is 90 degrees off then there is no head or tail wind component. However bear in mind that any strong wind will be affecting the aircraft by drifting and turning into wind will in effect mean that you have to fly a longer track than a straight line so it will slow you down a little bit.
If the wind is coming from behind you, then the same proportions can be applied to work out the tail wind component, so if it is 30 degrees off your tail, it is .9 of the strength of the wind and so on.
For working out a diversion, you can apply this percentage to your airspeed to get the groundspeed, and then to work out drift interpolate the following formula as well. The formula is that at 120 knots airspeed, half the cross wind component is drift. So if you are flying at 90 knots then your drift would be 25% more than half the drift.
This could be used if you need to work out your groundspeed and drift when planning an unexpected diversion.  Or when doing your flight planning, then you can use it to double check your calculations.