In the big picture I had a VERY good week on KA but it ended in a very disappointing way. 🫤 I’m SO happy to say that I not only got through the unit test for Unit 12, Inference for Categorical Data: Chi-Square, but I also made it through the AP College Statistics Course Challenge getting 28/30 questions correct, AND got through the two unit tests I needed to redo having gotten two questions wrong on the Course Challenge! 😭 🎉 At the start of the week I was fairly confident that I’d at least get through the first unit test, but I was doubtful that I’d pass the Course Challenge let alone finish off the entire course. I was riding a massive high getting through everything, but then I attempted the AB Calculus Course Challenge and… it didn’t go well. I only attempted one question but got it wrong which was super demoralizing and not the start I was hoping for. Getting one question wrong doesn’t sound that bad but, given that I already finished the Multivariable Calculus Course Challenge not that long ago, I thought I was going to walk through this Course Challenge. It makes me worried that finishing off AB and BC Calculus is going to take me way longer than I anticipated. 😔 But nonetheless, I’m still very happy with how this week went, overall, and am PUMPED to finally have stats behind me. 😮💨
I got through the Inference for Categorical Data: Chi-Square unit test on Tuesday afternoon. In total, I probably spent around 2 or 3 hours working on the test that day and got through it on my fourth attempt. I was pretty happy to pass it that day considering I’m guessing it’s been years since I last studied or looked at chi-squares tests. There were only 10 questions on the test and it was pretty easy overall, although I did get a few questions wrong and looked at KA’s answers which helped me review/remember what was going on. Here are three questions from the test:
AP College Statistics – Unit 9 – Unit Test – Sampling Distributions
Question 1
This was the first question I came up against on the test which I got wrong. I didn’t understand what needed to be done or what this question was asking. Looking at KA’s answer, I realized it’s asking, “Given that 40 of 120 people chose sprinkles, how many of the 48 adults surveyed would you have expected to get sprinkles?” The answer, as you can see, is 16 since (40/120) * 48 = 16.
Question 2
I got this question wrong not remembering what a Chi-square Goodness-of-Fit test was. (Also, what kind of stupid name is “Goodness-of-Fit”… 🤨) As you can see, the formula is pretty straightforward, and using the chi-square table is easy and pretty much the same as using a t-table.
Question 3
This was another question that I got wrong because I didn’t know/remember that the degrees of freedom for this type of stat is (rows – 1)(columns – 1). I thought it would be 49 since n = 50 and 50 – 1 = 49. But also, looking at KA’s answer, when I looked at my chi-square table saved on my computer, at DF = 2, the p-values jump from 0.9 to 0.1, so I couldn’t have even looked up what the p-value would have been at X2 = 3.06 because it’s 0.217 (as shown in KA’s answer) but that didn’t show up in the table I used… And when I looked up other chi-square tables on Google, they all showed the same thing. (I eventually found a website where I could input the chi-square statistic and the DF and it would tell me the p-value, but it was too-little-too-late at that point as I wasn’t given another question where I wasn’t able to answer it using the chi-square table I had on my computer.🤷🏻♂️)
After getting through that unit test, I then started the Course Challenge on Wednesday. Here are seven questions from the test:
AP College Statistics – Course Challenge
Question 4
This was the first question on the test. I got it correct remembering that I just needed to input the given values into the Stapplet website/calculator. To be honest, I wasn’t super confident that I had the right solution, that p = 0.067, but I assumed I’d done it correctly (and by “done” I mean inputted the values into the Stapplet calculator properly) and so I just went with 0.05 < P < 0.01 and was correct.
Question 5
This question seems like it’s from Grade 8 math, but I found it tricky because of the way the first bullet is phrased. I wasn’t sure if it meant 11 was supposed to go in the bottom right cell but I assumed it did (which was correct) and then the rest of cells were simple to solve after that.
(This question didn’t really seem worthy of adding to this post, but I hadn’t seen this type of question in either of my two attempts at this Course Challenge so I figured I’d add it just for funsies.)
Question 6
This was the 10th question on the test. I couldn’t think through that the answers were talking about so I guessed with c) and got it wrong. 😔 The reason why c) is wrong is because the LSR is below the data point at x = 6 and therefore the LSR underestimates it’s value, not overestimates it.
Question 7
I sort of half-cheated on this question. I looked up LSR output on Google to find a ŷ = b + ax image that showed me what b and a were, but that didn’t really help me. I checked my stats terms/notation cheat sheet and saw that SE = σ/√n but the LSR output showed the SE coeff. so I assumed 0.52 = σ/√n so there would be no need to redo √n the solution, i.e. the answer wasn’t a) or b). Somehow I figured out it would be a t-stat, so I opened my t-table to check what the significance level would be at n = 30 which turned out to be 2.75, so I assumed the answer was –5 (+/–) 2.75(0.52) because that made more sense than c) or d). I got lucky and it turned out I was correct. 🙃
Question 8
I couldn’t remember what “IQR outliers” were and, as you can see, I cheated on this question by Googling it and was shown the formula and explanation of it. 😑
Question 9
This was the 21st question of the test and it’s so simple/obvious but I got it wrong because I misread/misunderstood the table. 😡 I literally just misread the titles of each column and row and stupidly thought I just needed to divided 136/172 (but actually, looking at my answer of 0.76, that’s not even what 136/172 is, so I have no clue what I was doing…). As you can see, I just needed to know that ALL people surveyed chose one of the two options and therefore p = 1. SO DUMB!
Question 10
This was the final question on the Course Challenge. I had actually memorized the formula for σx̅ by this point, but I did double check it before answering. I’d also memorized that the population mean would be equal to μx̅, so I had that going for me which was nice. I answered this question correctly getting 28/30 in total and was SO relieved. 😮💨 😭
As I mentioned, I had to redo two unit tests after that from Unit 5 and Unit 7. I got through the first unit test in about 20 minutes and didn’t make any notes, but then got this question wrong on Unit 7’s unit test:
AP College Statistics – Unit 7 – Unit Test – Probability
Question 11
I got this question wrong not really understanding what the question was asking. I assumed I had to divide two of the three givens but didn’t understand which ones I was supposed to divide. I went P(Jan)/P(6 months) when, as you can see, I should have gone P(6 months & Jan.)/P(Jan).
As I said in my intro, I opened up and attempted the first question on the AB Calculus’s Course Challenge and got it wrong. 😒 This was the question:
AB Calculus – Course Challenge
Question 12
Honestly, I don’t remember this proof so I’m not going to bother trying to explain it or talk about it here. But suffice it to say, I was very demoralized when I got this wrong…
And that was it for this past week. I’m feeling good and bad at the same time about where I’m at with all of this. It really depends on how the AB Calculus Course Challenge goes at the start of this coming week. If I’m able to get 25-ish questions correct, I won’t be too upset. But if I get much more than that wrong, I’ll be annoyed that I’ll have to redo a bunch of unit tests and frustrated that I’ve come so far without being able to solve the questions in AB Calculus (let alone BC Calculus). So more than ever, fingers tightly crossed that I can have a solid, productive, and successful upcoming week so I can make some decent progress getting through this second last course and be ONE COURSE AWAY from finishing off this 6.5 year goal/journey. 😭🤞🏼🙏🏼