Normally I cant be asked to calculate stuff, so this is what I do:
1-Align your course indicator with the inbound track of the hold
2-Place your pencil/pen on the HSI and position it so its in the centre of the instrument.
3-for standard holds (left) the pen/pencil should be 70 degrees to the right of your heading. You have now divided the HSI in two.
4-And now imagine a line coming down from your current heading to the centre. You have now divided the HSI in 3; a section that is 70 degrees, the next section is 180 degrees, and the last section is 110 degrees.
5-The tail of your course indicator will be in one of these sections, that will correspond to the hold entry. 70 deg. section= teardrop, 180 deg. sect.= direct, and 110 deg.= parallel
Hope this makes sense!, and that it helps
Good luck