Chapter 5 - Section 5.3 - Assess Your Understanding - Applying the Concepts - Page 285: 22b

$P(at~least~one~test~will~not~be~positive)=0.113615$

The event "at least one test will not be positive" is the complement of "all 12 tests will be positive". So, we use the Complement Rule (see page 275): $P(at~least~one~test~will~not~be~positive)=$ $=1-P(all~12~tests~will~be~positive)=1-0.886385=0.113615$