Chapter 5 - Section 5.3 - Assess Your Understanding - Applying the Concepts - Page 284: 15b

$P(positive~for~at~least~one~of~the~five~people)=0.02475$

The event "ELISA comes back positive for at least one of the five people" is the complement of "ELISA comes back negative for all five people". So, we use the Complement Rule (see page 275): $P(positive~for~at~least~one~of~the~five~people)=$ $1-P(negative~for~all~five~people)=1-0.97525=0.02475$