Given her evaluation of current economic conditions, Ima Nutt believes there is a 50 percent probability of recession, a 20 percent change of continued steady growth, and a 30 percent probability of inflationary growth. For each possibility, Ima has developed an interest rate forecast for long-term Treasury bond interest rates accordingly: 6%, 9% and 14%. What is the standard deviation under Imas interest rate forecast?

9.0%

2.91%

3.46%

0.12%