Sets 3

2 marks · Easy

In a club of 50 members, 32 members play chess (set C), 19 members play cards (set D), and 7 members play both chess and cards. Use set notation to calculate the number of members who play only chess.

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25 members play only chess members (±0)

Must show: Find n(C ∩ D′)

Also accept: Writing answer as n(C \ D) or n(C ∩ D′) = 25

Common mistakes: Subtracting incorrectly (e.g., not taking away the intersection)

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Marking points

M1 · 1 mark · Writes n(C ∩ D′) = n(C) − n(C ∩ D) or similar correct set operation.

A1 · 1 mark · Carries out the subtraction: 32 − 7 = 25. (follow-through)

Worked solution

Members who play only chess are in C but not in D, so n(C ∩ D′) = n(C) − n(C ∩ D).