Consider an economy with two types of? firms, S and I. S firms all

move together. I firms move independently. For both types of firms there is a 43 % probability that the firm will have a 8 % return and a 57 % probability that the firm will have a negative 2 % return. What is the volatility? (standard deviation) of a portfolio that consists of an equal investment? in:
a. 15 firms of type? S?
b. 15 firms of type? I?