In a class of 70 students, 34 like Physics, 30 like Chemistry and 28 like Biology. 12 like both Physics and Chemistry, 10 like both Physics and Biology, 9 like both Chemistry and Biology, and 4 like all three subjects (each ‘both’ count includes these 4). How many students like exactly one of the three subjects?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 42
The students who like only one subject are found circle by circle: from each subject total take away the two ‘both’ counts of that subject, and add back the 4 who like all three, as they were taken away twice.
Physics only \(=34-12-10+4=16\)
Chemistry only \(=30-12-9+4=13\)
Biology only \(=28-10-9+4=13\)
Exactly one subject \(=16+13+13=42\)
