This is a classic three-set overlapping problem - these can definitely be tricky until you see the key insight. Let me walk you through this step-by-step.
The Key Insight You Need:When the problem says "7 play both Hockey and Cricket," this includes students who might also play Football! This is where most students get confused. Let's think about this systematically.
Step 1: Set Up Your Known ValuesLet's organize what we know:
- Total students = 50
- Students playing NO sports = 18
- Therefore, students playing at least one sport = \(50 - 18 = 32\)
Individual sports:
- Hockey (H) = 20
- Cricket (C) = 15
- Football (F) = 11
Overlaps (at least two sports):
- H and C = 7
- C and F = 4
- H and F = 5
- All three = ? (let's call this \(x\))
Step 2: Use Inclusion-Exclusion to Find Students Playing All ThreeHere's what you need to see - when we add all the individual sport players (\(20 + 15 + 11 = 46\)), we're counting some students multiple times.
Using the inclusion-exclusion formula:
\(|H \cup C \cup F| = |H| + |C| + |F| - |H \cap C| - |C \cap F| - |H \cap F| + |H \cap C \cap F|\)
Substituting our values:
\(32 = 20 + 15 + 11 - 7 - 4 - 5 + x\)
\(32 = 46 - 16 + x\)
\(32 = 30 + x\)
\(x = 2\)
So 2 students play all three sports!
Step 3: Calculate Exactly Two SportsNow here's the crucial part - to find students playing
exactly two sports, we subtract those playing all three from each pair:
- Exactly Hockey and Cricket (not Football): \(7 - 2 = 5\)
- Exactly Cricket and Football (not Hockey): \(4 - 2 = 2\)
- Exactly Hockey and Football (not Cricket): \(5 - 2 = 3\)
Total playing exactly two sports: \(5 + 2 + 3 = 10\)
Answer: B (10 students)Notice how the trick was recognizing that the given overlaps included the "all three" students? That's the pattern you want to watch for in these problems.
You can check out the
step-by-step solution on Neuron by e-GMAT to master the inclusion-exclusion principle systematically and learn a powerful verification technique that ensures you never make calculation errors. You can also explore other GMAT official questions with detailed solutions on Neuron for structured practice
here.