In a certain medical survey, 45% of the people surveyed had the type A antigen in their blood and 3%...

1. Translate the problem requirements: We need to find what percent of people with type A antigen also have type B antigen.
2. Identify the given information: Extract the key percentages from the survey data.
3. Set up the conditional relationship: Recognize this as a part-of-a-part calculation.
4. Calculate the percentage within the group: Divide the percentage with both antigens by the percentage with type A and convert to percent form.

Execution of Strategic Approach

1. Translate the problem requirements

The question asks: "Which of the following is closest to the percent of those with the type A antigen who also had the type B antigen?" In other words, of all people with type A, what fraction also have type B?

2. Identify the given information

• 45% of all surveyed have type A antigen
• 3% of all surveyed have both type A and type B antigens

3. Set up the conditional relationship

Of the 45 people (per 100) with type A, 3 have both. So we compute 3 ÷ 45.

4. Calculate the percentage

\(3 \div 45 = \frac{1}{15} = 0.0667…\)
\(0.0667 \times 100\% = 6.67\%\)

Final Answer

6.67% (answer choice B)