Sets 3

3 marks · Normal

In a set of 32 students, 18 study Physics (P), 15 study Chemistry (C), and 7 study both subjects. Work out the number of students who study either Physics or Chemistry, but not both.

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19 (±0)

Common mistakes: Adding all students (18 + 15) without subtracting the overlap; Including those who do both in both 'only' counts

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Marking points

M1 · 1 mark · Calculates the union: 18 + 15 - 7.

M2 · 1 mark · Subtracts the number who study both to find only one subject: (18-7) + (15-7) = 11 + 8.

A1 · 1 mark · Arrives at 19 students.

Worked solution

Number who study only Physics: 18 - 7 = 11.

Number who study only Chemistry: 15 - 7 = 8.