Four lessons in, you can talk a skeptical relative through blockchains, swat away the “my wallet holds my coins” myth, trace a payment from send to confirmed, and tell a UTXO from an account balance. This is where the talk gets tested. No fresh diagrams, no warm-up — just the ideas you already learned, dressed up with the kind of almost-right traps that catch people who only think they get it.
How this exam works
This is a graded exam. Questions come one at a time. Once you submit an answer it is final — there is no going back, no second try, and a wrong answer simply fails that question. Your score stays hidden until the end, where you need 70% to pass. Read every option twice before you commit.
A blockchain exists mainly to solve which problem?
Select an answer to continue.
Course Recap
Big picture
Crypto, from scratch — the complete map
- Crypto, from scratch
- What a blockchain is
- Append-only, tamper-EVIDENT ledger (not secret)
- Blocks linked by the previous block’s hash
- Hash = one-way fingerprint; any change cascades
- Replicated across nodes; consensus picks one chain
- Keys & wallets
- Wallet stores KEYS, not coins (coins live on the ledger)
- Private key signs & stays secret
- Public key/address is safe to share
- Seed phrase = the only recovery, no reset
- Not your keys, not your coins (hot vs cold)
- Transactions & fees
- Sign → broadcast → mempool → block → confirmations
- Block space is scarce
- Higher fee = faster inclusion (an auction)
- Fee goes to the block producer, not the receiver
- Gas ≈ computation; congestion spikes fees
- UTXO vs account
- UTXO (Bitcoin): discrete coins, change returns, balance = sum
- Account (Ethereum): one running balance + nonce
- UTXO: parallel, replay-proof, but coin selection is fiddly
- Account: simpler, contract-friendly, global-state bottleneck
- What a blockchain is
Key Takeaways
What to remember
You’ve genuinely finished this course if you can, without peeking:
- Say what a blockchain is — an append-only, tamper-evident (not encrypted) ledger, blocks linked by the previous block’s hash, replicated across nodes, one shared chain chosen by consensus — and explain why “blockchain = Bitcoin” and “it’s a central database” are both wrong.
- Explain who owns a wallet — it holds keys, not coins; the private key signs and stays secret; the address is safe to share; the seed phrase is the only recovery with no reset; and “not your keys, not your coins” separates self-custody from a custodial exchange.
- Trace a transaction — sign → broadcast → mempool → block → confirmations; know that block space is scarce, fees are an auction that pays the block producer (not the receiver), gas measures computation, and one confirmation isn’t true finality.
- Tell UTXO from account — Bitcoin’s discrete coins spent whole with change returned (balance = sum of UTXOs) versus Ethereum’s single running balance ordered by a nonce — and recite the trade-offs without ever calling change a “loss.”
Aced it? You now understand the machinery under every coin and every DeFi app — exactly what you need before going deeper. Pick your next ladder and keep climbing.