**UCAT/ UKCAT Question Analysis - Decision Making Question 2**

This year, 40% of the population received the flu vaccine. Yet, 70% of the populatiobn caught the flu. **Which of the following MUST be true?**

A. At most 10% of those vaccinated caught the flu.

B. At least 25% of those vaccinated caught the flu.

C. At most 10% of the population was vaccinated and caught the flu.

D. At least half of those who were not vaccinated stayed healthy.

**Answer and Explanation:**

**B. ****At least 25% of those vaccinated caught the flu.**

This type of question is often BEST solved by using simple graphs.

By juxtaposing graphs in accordance with each option, you can determine whether each statement is correct or not.

From Graphs 1 and 3, we know that those who caught the flu have to re[resent at least 40% - 30% = 10% of the population. This is equivalent to 10/40 = 25% of the vaccinated population.

Take a look at the other options:

**A. At most 10% of those vaccinated caught the flu.**

From Graphs 1 and 2, it is possible that all 40% vaccinated actually caught the flu. So, we can't say that most 10% of those vaccinated caught the flu as it could be as high as 100%.

**C. At most 10% of the population was vaccinated and caught the flu.**

We know from the reasoning used for A that this could be as high as 100%. However, it is true that AT LEAST 10% of the po;ulation was vaccinated and caught the flu.

**D. At least half of those who were not vaccinated stayed healthy.**

Graphs 1 and 3 show that it is possible that all non-vaccinated people caught the flu. However, AT MOST half of those who were not vaccinated stayed healthy.

Drafted by Quincy (UCAT Prep)

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