Openai/691cc483-9e74-8006-a4a7-7e5bbf8a5391

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gpt-5-1

Assistant: Alright, let’s cut straight through it.

Alright, let’s cut straight through it.

What’s happening? They keep picking two numbers and replacing them with (sum − 2). That means:

• Every operation reduces the total sum by exactly 2.
• They start with numbers from 3 to 89, inclusive.

Step 1 — Count how many numbers there are

From 3 to 89:

89−3+1=87 numbers89 - 3 + 1 = 87 \text{ numbers}89−3+1=87 numbers To end with one number, they must do:

87−1=86 operations87 - 1 = 86 \text{ operations}87−1=86 operations

Step 2 — Compute the initial sum

Sum of an arithmetic progression:

S=(3+89)⋅872S = \frac{(3+89)\cdot 87}{2}S=2(3+89)⋅87​ =92⋅872=46⋅87=4002= \frac{92 \cdot 87}{2} = 46 \cdot 87 = 4002=292⋅87​=46⋅87=4002

Step 3 — Decrease the total sum

Each operation subtracts 2, and there are 86 operations:

4002−2⋅86=4002−172=38304002 - 2\cdot 86 = 4002 - 172 = 38304002−2⋅86=4002−172=3830

Final answer:

3830

That’s the last number standing.