Chapter 7 - Section 7.1 - Assess Your Understanding - Vocabulary and Skill Building - Page 367: 13b

There is 40 percent probability that the friend will arrive within the next 12 minutes (or by 10:12 am).

$\frac{40}{100} \times 30 = 12$ There is 40 percent probability that the friend will arrive within the next 12 minutes (or by 10:12 am). (Because the value of the random variable is between 0 and 30 the probability for every minute is $\frac{1}{30}$)