Answer: Hello mate!
There are 100 students, and each one has the same probability of being selected, which is 1/100
The chances that the band leader selects you is 1/100
now the chances that the band leader selects your brother is one over the total number of people in the band, but you have already been selected, so there are 99 people right now in the band, this probability is of 1/99.
The joint probability of both events is the product of the probabilities, this is:
P = (1/100)*(1/99) = 1/9900
But there is also the chance where your brother is picked first and you second, which also has a probability of 1/9900.
Then the total probability of you and your brother to being selected is:
P = 1/9900 + 1/9900 = 2/9900 = 1/4950
te right option is option C.
