1) Imagine an attacker has amassed 20% of the network's hash power, and is looking to trick someone by double spending a 1-confirmation transaction.

He sends 10btc to Bob, Bob waits for 1 confirmation, and sends the attacker some other cryptocurrency in exchange.

Now the attacker creates an alternative transaction that spends the same coins to himself instead, and has to create a block containing his double-spend transaction, as well as another block based on that previous one, in order to create a 'longest chain' containing his double spend.

What is his probability of succeeding? Enter answer in percents, accurate to two decimal places.

2) In the previous problem, Bob decides to wait for 3 confirmations before sending the attacker his goods. Now what is the attacker's probability of successfully double-spending against Bob?

Enter answer in percents, accurate to two decimal places.