a.There are 100 pieces of string in my pocket.Each one is between 10 and 20 cm long.If I pull out 30 at random and lay them end to end, what is the probability that the resulting length of string would be more than 480 cm long?

b.When I was young, my brother claimed to be psychic.He claimed he could correctly identify a coin toss more often than he should.We tested this with 30 tosses, of which he guessed correctly 20 times.Is this good evidence?