Duration: 40 minutes | Points: 20 | Format: Teams of 3-4
Learning Objectives
- Understand the structure and constraints of blockchain blocks
- Apply fee prioritization strategies to maximize miner revenue
- Experience the economic incentives that drive block production
- Learn simplified block hashing and verification mechanisms
- Recognize trade-offs between transaction inclusion and block space limits
Overview
You are a blockchain validator (miner) tasked with building the next block. You have access to 20 pending transactions in the mempool, each with different fees and sizes. Your goal is to select transactions that maximize your total fee revenue while respecting the block size limit.
Block Constraint: Maximum block size = 10 units
Team Formation
Work in teams of 3-4 students. Each team represents a competing validator trying to build the most profitable block.
Activity Timeline (40 Minutes)
5 min Phase 1: Setup & Transaction Review
- Receive your transaction cards deck (20 cards)
- Receive blank block template worksheet
- Review all available transactions and their properties:
- TX ID: Unique transaction identifier (tx_001 - tx_020)
- Fee: Amount paid to validator (in ETH)
- Size: Block space consumed (in units)
- Discuss initial strategy with your team
20 min Phase 2: Block Construction
- Sort and analyze transactions to identify high-value options
- Calculate fee-per-unit ratios to guide selection
- Select transactions for your block (record on template):
- List each selected transaction by TX ID
- Record corresponding fees and sizes
- Ensure total size does NOT exceed 10 units
- Calculate your total fee revenue
- Double-check all calculations
10 min Phase 3: Block Hashing & Verification
- Compute your block hash using the simplified formula:
- Extract the last digit from each selected TX ID
- Sum all last digits
- This sum is your "block hash"
- Example: tx_007, tx_013, tx_020 → 7 + 3 + 0 = 10
- Record the hash on your block template
- Verify with hash guide if needed
- Have another team verify your block is valid:
- Size constraint respected (total ≤ 10)
- Fee calculation correct
- Hash calculation correct
5 min Phase 4: Preparation for Presentation
- Prepare to explain your selection strategy
- Identify which transactions you prioritized and why
- Note any difficult trade-offs you encountered
- Prepare one team member to present
Presentation Format (5 Minutes per Team)
Each team will present to the class:
- Strategy (2 min): Explain your transaction selection approach
- Results (1 min): Share total fees, block size, and hash
- Trade-offs (1 min): Discuss difficult decisions you made
- Q&A (1 min): Answer questions from instructor and peers
Winning Criteria
| Criterion | Description |
|---|---|
| Highest Total Fees | The team with the highest valid total fee revenue wins |
| Valid Block | Block size must be exactly 10 units or less |
| Correct Hash | Hash must be correctly calculated per formula |
Tip: High fees matter, but so does efficient use of block space. A transaction with a
moderately high fee but small size might be better than a slightly higher fee with large size!
Key Concepts to Consider
- Fee Density: Fee per unit of block space (Fee ÷ Size)
- Opportunity Cost: Including a large transaction means excluding multiple smaller ones
- Knapsack Problem: This is a classic optimization challenge in computer science
- Miner Incentives: Real validators face these same economic trade-offs
Materials Checklist
- Transaction cards deck (20 cards)
- Block template worksheet
- Hash calculation guide
- Calculator (optional but recommended)
- Pencil and eraser for revisions
Submission Requirements
Submit your completed block template worksheet with:
- Team member names
- List of selected transactions
- Total fee calculation
- Total size calculation
- Computed block hash
- Verification signature from another team
Related Resources
Assignment Resources
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