Chapter 10 Counting Methods and Probability - 10.3 Define and Use Probability - 10.3 Exercises - Skill Practice - Page 702: 19

Option C

There are 7 months that have 31 days. The probability of choosing the first month that has 31 days is: $P_1=\frac{7}{12}$ For the second month, we have to choose from the remaining 6 months that have 31 days and the other 11 months. The probability then will be $P_2=\frac{6}{11}$ The probability that two randomly selected months have 31 days is: $P=P_1.P_2=\frac{7}{12}.\frac{6}{11}=0.318$ Hence, the correct option is C.