You are reviewing a list of 8 recommended securities and wish to invest in 4. You will put 40% of your capital in one, 30% in another, 20% in the third, and 10% in the last one. How many different ways can you choose among the 8 securities and invest according to your design?
Correct Answer: C
The combination, or binomial formula, gives the number of ways that k objects can be chosen from n items, without regard to the order of choosing. The formula is (n choose k) = n! / [k! *(n-k)!].
However, in this case, the order does matter. If we choose stocks 3, 1, 7, and 5, we don't consider that the same as choosing 5, 7, 1 and 3, because the portfolio weights would differ. We need the general permutation formula, which gives the number of ways that k objects can be chosen from n items, with regard to order. The formula is n_P_k = n! / (n-k)!. Here, it is 8! / (8-4)! = 8 * 7 * 6 * 5 = 1,680.