My 6th grader had this problem on yester
Ask
My 6th grader had this problem on yesterday's math homework:
"Find the mean of the four science quiz scores: 85, 90, 0, 95."
He added them up correctly to 270, but then divided by 3 to get 90. When I asked why he divided by 3 when there are four scores, he argued: "The third quiz is a zero! Zero is nothing, so it doesn't count as a score!"
We live in Seattle, WA (America/Los_Angeles timezone), and today is Friday, Sep 25, 2026.
Could you record this into our mistake notebook as a strict 5-line card (题面, 错法, 修法, tag, 错因) and schedule a daily 19:00 review reminder? We plan to review it tonight.
Answer
I'll record this as a 5-line card and set up the reminder. Let me check the references first and see what's already in the notebook.
The notebook already has 36 unreviewed cards (reps=0) queued as due today — I'll mention that after recording your new one.
The reminder couldn't be added — you've hit the cap of 20 active schedules. Let me show what's there so you can decide which one to free up.
Card recorded — but I couldn't add the daily 19:00 reminder. Here's the full picture.
## Card (5 lines)
| Line | Field | Content |
|---|---|---|
| 1 | **Prompt** | Find the mean of the four science quiz scores: 85, 90, 0, 95. |
| 2 | **Wrong move** | Divided 270 by 3 to get 90, arguing "zero is nothing, so it doesn't count as a score." |
| 3 | **Right move** | Mean = sum ÷ count of **all** scores the quiz recorded (here, 4 — including the zero). 270 ÷ 4 = 67.5. **Same-type:** mean of 70, 80, 0, 90, 100 → 340 ÷ 5 = 68. |
| 4 | **Tag** | `mean` |
| 5 | **Cause** | Confused count of all values with count of non-zero values; treated a score of 0 as "no score" and dropped it from the divisor. |
- id: `f8808a923c165b33`
- first due: 2026-09-26 (tomorrow)
## About the daily 19:00 reminder
It was not set — your account already has **20 active schedules (the cap)**, and **nine of those are already daily at 19:00**. So one of three things is true:
1. One of those existing 19:00 slots is *already* the mistake-notebook review reminder → you're covered, nothing to do.
2. You have multiple 19:00 reminders and some are duplicates you no longer need → tell me the schedule_id to disable, and I'll add the review one.
3. None of them is the review reminder and you'd like to repurpose one → same as #2: pick one to disable, I'll create the review one in its place.
The 9 currently enabled at 19:00 daily (Seattle local) are:
`b349964d…`, `3ec251a1…`, `8a665f1b…`, `a33d98ab…`, `94a0833e…`, `b3d77233…`, `f0332b6b…`, `cab23cb3…`, `7e266918…`
Tell me which to disable (or "none of these is the review one, free up `…`"), and I'll set the new one in its place.
## One thing about "tonight's review"
This card isn't alone in the pile — the notebook already has **36 unreviewed cards (reps = 0) queued as due today**, so the new card makes it **37 cards tonight, not 1**. If you want, I can pull the full list and group by tag so the session has a shape; just say the word.
For tonight's self-test on *this* card: book closed, child tries "mean of 85, 90, 0, 95" from memory → then we reveal the right move and mark pass/fail. That's the one due tomorrow — the rest of the 36 will have their own reveal moments.