2017 AMC 12B — Practice Log
Quick reflections and timing notes.
Q1–Q23: all correct ✅
Q22: time sink ⏳
Q24–Q25: not answered ❌
Notable Questions
- #13: Took me a while; need to keep practicing Burnside's lemma/technique. (note to self: revisit topic & drill)
- #22: Became a time sink. Pause sooner; sketch structure, estimate difficulty, and decide quickly whether to skip.
- #24: Didn’t understand the question—unclear how to set up the average. Re-read carefully; translate wording to variables first.
- #25: Ran out of time.
Process & Timing Notes
- Not enough time at the end—was able to draw the diagram but didn’t complete the setup.
- For average/setup questions: define variables immediately, write the equation before computing.
- When a problem starts ballooning (>3–4 minutes without structure), mark and move.
Follow-Up Plan
Thursday, September 11, 2025
Dimentional Change Questions III: Similar Shapes
There are numerous similar triangle questions on Mathcounts.
Here are the basics:
Many students have trouble solving this problem when the two similar triangles are superimposed.
\(\frac{BC}{DE}\)= \(\frac{AB}{AD}\) = \(\frac{AC}{AE}\)
Questions to ponder (Solutions below)
#2: Find the volume of the cone ABC to Frustum BCDE to DEGF to FGIH. Again, you can use the similar cone, dimensional change property to easily get those ratios.Same conditions as the previous question.
Here are the basics:
If two triangles are similar, their corresponding angles are congruent and their corresponding sides will have the same ratio or proportion.
Δ ABC and ΔDEF are similar.
\(\frac{AB}{DE}\) = \(\frac{AC}{DF}\) = \(\frac{BC}{EF}\)= their height ratio = their perimeter ratio.
Once you know the linear ratio, you can just square the linear ratio to get the area ratio and cube the linear ratio to get the volume ratio.
Once you know the linear ratio, you can just square the linear ratio to get the area ratio and cube the linear ratio to get the volume ratio.
Practice Similarity of Triangles here. Read the notes as well as work on the practice problems. There is instant feedback online.
Many students have trouble solving this problem when the two similar triangles are superimposed.
Just make sure you are comparing smaller triangular base with larger triangular base and smaller triangular side with corresponding larger triangular side, etc... In this case:
Questions to ponder (Solutions below)
#1: Find the area ratio of Δ ABC to trapezoid BCDE to DEGF to FGIH. You can easily get those ratios using similar triangle properties. All the points are equally spaced and line \(\overline{BC}\)// \(\overline{DE}\) //
\(\overline{FG}\) // \(\overline{HI}\).
#2: Find the volume of the cone ABC to Frustum BCDE to DEGF to FGIH. Again, you can use the similar cone, dimensional change property to easily get those ratios.Same conditions as the previous question.
Answer key:
#1:
#2:
Monday, September 1, 2025
9/1/2025 Student Reflection Note from H
2018 AMC 12A Notes 🎉
😊 Only 2 Wrong — Great Job!
Wrong
- 22: Not sure how to express √abi cleanly.
Couldn’t manage complex numbers or split the area into 4 pieces. - 25: Was able to get the powers of 10 and simplify, but not the final casework step.
Right
15, 16, 17, 18, 19, 20, 21, 23, 24
8/31/2015 Student reflection notes from H
2019 AMC 12B Notes
Problems 20–25 → Wrong
- 20: Tried coordinate bash but didn’t realize AOBX is cyclic.
- 21: Very close, but made a mistake in casework.
- 22: No idea how to estimate.
- 24: Confusing — unsure how to approach.
- 25: Imaginary numbers solution was smart.
Also homothety solution was smart too.
Problems 15–19, 23 → Right
Saturday, August 23, 2025
8/23/2025 student reflection notes from H ～ Welcome back to the States.
2019 AMC 12A – Reflection Log
Quick notes on misses, themes, and time sinks.
Incorrect
- #22. Problem and Solutions
- #24. Found all prime exceptions but missed 4 — Problem and Solutions
- #25. Got after hint → need work on angle chasing in cyclic quadrilaterals — Problem and Solutions
Correct
Problems solved:
#15
#16
#17
#18
#19
#20
#21
#23
- #17 → learn Newton's Sums
- #23 → algebra took a long time.
Next Steps
- Drill Newton’s Sums identities; derive first 3–4 power sums using Vieta.
- Re-check prime-exception logic; include 2 and 4 in prime-exception checklist.
- Daily 10-min cyclic quadrilateral angle-chasing (use Ptolemy, equal angles, arc marks).
- Practice pacing to avoid #17-style time sinks; enforce a 2-minute “move on” rule.
- Algebra endurance reps (substitution, factoring patterns), especially for de-jangling #23-type problems.
