p sample, july 18
| date | page | question | duration | ans | result | thoughts |
|---|---|---|---|---|---|---|
| 2025-07-18 Fri 13:13 | 44 | 98 | 4 | b | ✅ | |
| 99 | 7 | e | ✅ | |||
| 167 | 406 | 10 | e | ✅ | ||
| 407 | 8 | c | E | median, not mean; also forgot variance | ||
| 216 | 525 | 9 | b | ✅ | ||
| 526 | 6 | e | C | |||
| 102 | 241 | 12 | e | ✅ | ||
| 242 | 5 | b | E |
What the heck, man?
407. A memoryless distribution.
I had the right logic here. But I missed that the parameter in the question was the median rather than the mean. Argh.
526. Many zones with tornado risk.
Wrong result for the variance of many groups. I knew this one. I got it right before. But this time I messed it up.
Remind myself again. Expectation values go like
$$\begin{aligned} E(aX + b) = a\, E(X) + b \\ \end{aligned}$$
Oh, I see what I misremembered. For the independent systems, the variances add linearly.
Blugh.
242. A combined continuous $\times$ discrete distribution
I use the variance when I should have used the "second moment."