Hypothesis Testing

Hi, i was hoping to get help with this question:
Miss Cackle wishes to decrease the percentage of pupils giving up her potion-
making class after year 9 from its current level of 20%. Over the last 3 years she
has tried a new teaching method in one of her classes of 30 pupils, Using a 10%
significance level find the critical region for a test of whether the number of
pupils giving up potions after year 9 has decreased. State the actual significance
level.

What have you done so far / what are you stuck with?

I'm not sure on how to set out my answer so I'm really stuck on how to approach it and what to do T_T

Is it one tailed or two tailed, what distribution, ...?

I'm presuming it's a one tail test as she's trying to see if the number of pupils had decreased?

Agreed, so what is the actual test/level?
And as in the the previous post, which distribution and what are the parameters?

so the binomial distribution would be X~B (30, 0.15)
the

Why 0.15?

sorry, is it 0.2?

Of course. You must have several similar examples to this in your textbook and you should be able to write this down (even with the odd error) without me having to prompt you.

maybe I should have made myself more clear from the start, I had actually already figured out the distribution and hypothesis for the question as that is how you always approach these. But my main issue with the question is how to calculate the critical region so please can you explain that to me? Also the 'odd error' i made was because I was looking at a previous example I had done.

Hi, i was hoping to get help with this question:
Miss Cackle wishes to decrease the percentage of pupils giving up her potion-
making class after year 9 from its current level of 20%. Over the last 3 years she
has tried a new teaching method in one of her classes of 30 pupils, Using a 10%
significance level find the critical region for a test of whether the number of
pupils giving up potions after year 9 has decreased. State the actual significance
level.