Chapter 5 - Section 5.2 - Assess Your Understanding - Applying the Concepts - Page 279: 45b

P(45 to 54 years of age) $=\frac{14}{53}\approx0.264$

The sample space: 530 adult Americans. So, N(S) = 530. According to the marginal distribution (see definition, page 235) of the third column: N(45 to 54 years of age) = 140. P(45 to 54 years of age) = $\frac{N(\text{45 to 54 years of age})}{N(S)}=\frac{140}{530}=\frac{14}{53}\approx0.264$