whenever ur given a population / number of trials that is like NOT huge you should use the sample population formula since things act more eratically at low samples
for example if i flip a coin 20 times, theres a very low chance it behaves as a normal distribution, however if i flip it 2,000,000 times then the normal curve will come about,
so in those cases where the normal curve isnt basically guaranteed, i.e youre given a population, number of trials that satisfy
np ≥ 10 and n(1−p) ≥ 10 <--- this is not a math rule this is just a rule of thumb, itll be very clear in the HSC what they want
then u can use sample