I am a little bit confused about the margin requirements for short Options in Chapter 5 of the GARP book (i am working with the 2020 version). I am not sure if there is a mistake or if i am just missing something. GARP states, that the requirement for a short call is calculated as the greater of:

a) 100% of value of option plus 20% of underlying stock price less amount ( if any) that the option is OTM

b) 100 % of value of option plus 10% of underlying stock price

for a short put the requirements are the same for a) but in b) the stock price is replaced by the strike price

The given example is: 100 call options on a stock are sold for USD 5 per Option when stock price is USD 47. When strike price is USD 50 the option is USD 3 out-of-the money.

the calculated margin is

max(5+0.2x47-3,5+0.1x50)=11.4 in the second part of the Max-Function the strike price is used but this would be the function for a short put not a short call (in case of short call it must be 5+ 0.1x47 (the stock price) as stated above).

Are the formulars correct an there is just an error in the example or are the margin requirements for short call and short put identical and the part b) formula for a short call is wrong? I could not find it in the study notes, maybe i just overlooked them.

Thanks in advance

Nina