plz show the full solution with clear hand writing

P6.2 At the start of Tom Stoppard's "Rosencrantz and Guildenstern are dead" 1 , Rosencrantz finds a coin. Guildenstern watches as Rosencrantz repeatedly tosses the coin and every time it comes down heads 2. Guildenstern believes that one in a thousand coins found like this are magic and always come down heads, and the rest are unbiased. After how many tosses should Guildenstern be 99% certain that his friend's coin is a magic one