360 vs 365 day years

CFA Level I Derivatives
#1

Be it derivatives or quant or any topic. T-bills use 360 day year by convention. Then, LIBOR. Then, there are Eurodollar deposits - as they are based on LIBOR, so they use 360.

Can anyone help distinguish which instruments use 360 and which 365? And is this relevant for CFA L1 exam purpose?

Q. Calculate the payoff at expiration for a call option on an interest rate in which the underlying is a 180-day interest rate at 6.53 percent at expiration, the notional principal is $10 million, and the exercise price is 5%. what should be used? 360 or 365? (The answer uses 360. WHy?

#2

CFA Institute assumes that the underlying on interest rate options is LIBOR: 360 days.

#3

In my experience, you should be able to glean the correct answer, even if you use the wrong day count convention.