suppose that empirical data  suggest an individual requires an average return of 0.5 percent if he or she is to be tempted to invest in an invesment that has 50-50 chance of gaining or losing 5 percent.
这是尼那本书地十八章课后第八题的第三问的题干的一部分，感觉不好理解，谁能帮忙解释一下