Great question to practice — this one is testing constrained permutations with complementary counting, which is exactly the kind of setup that trips people up in Two-Part Analysis because you have to nail both values independently.
Key concept being tested: Restricted arrangements using complementary counting (total minus the "forbidden" cases).
Step 1 — Understand the structure.
Team Legato has 1/4 as many members as Team Forte. With 20 duos in the competition and a 1:4 member ratio, Legato accounts for 4 duos and Forte for 16 duos. Prizes go to the top 3 duos overall.
Step 2 — Part 1 (20 duos): No sweep, Legato must come 1st.
Start with the restriction you know for certain: Legato wins 1st. That gives 4 choices (one for each Legato duo).
Now fill 2nd and 3rd from the remaining 19 duos. Use complementary counting:
- Total ways to arrange 2nd and 3rd: P(19, 2) = 19 × 18 = 342
- Subtract cases where Legato "sweeps" (2nd and 3rd also from Legato): P(3, 2) = 3 × 2 = 6
- Valid arrangements for 2nd/3rd: 342 − 6 = 336
Total for Part 1: 4 × 336 = 1,344 → closest to 1 Million.
Note: since Legato is already locked into 1st, a Forte sweep is impossible — you only need to remove the Legato sweep cases. This is where most students waste time applying a much more complicated restriction than needed.
Step 3 — Part 2 (10 duos): Half as many participants.
With 10 duos (2 Legato, 8 Forte), same setup:
- Legato wins 1st: 2 choices
- Remaining 9 duos for 2nd and 3rd. Only 1 Legato duo left — a Legato sweep of 2nd+3rd is impossible with just 1 remaining Legato duo.
- So: P(9, 2) = 9 × 8 = 72, no subtractions needed.
- Total: 2 × 72 = 144 → closest to 10,000.
Common trap: Students apply the no-sweep restriction globally — removing all cases where any one team wins all 3 medals — instead of recognizing that since Legato is already locked into 1st, only a Legato sweep remains possible. This drastically simplifies the calculation.
Takeaway: In TPA permutation problems, lock in the fixed constraint first, then apply complementary counting only to the remaining open positions.
— Kavya | 725 (99th percentile), GMAT Focus