50 people attended an outdoor activity day - OCR - GCSE Maths - Question 16 - 2019 - Paper 1

To find the probability that a person who walked also sailed, we first need to determine how many of the 40 people who walked also participated in sailing.

Let’s denote:

• Total participants = 50
• Participants who did neither = 3

Thus, participants who did either walking or sailing:

$50 - 3 = 47$

Next, we know:

• Participants who walked = 40
• Participants who sailed = 18

Using the principle of inclusion-exclusion:

$ext{Participants in either walking or sailing} = ext{Participants who walked} + ext{Participants who sailed} - ext{Participants who both walked and sailed}$

Therefore:

$ext{Participants who both walked and sailed} = 40 + 18 - 47 = 11$