A set of 4 parallel lines intersect with another set of 5 parallel lines. How many parallelograms are formed? A. 20 B. 48 C. 60 D. 72

GATE 2018 · General Aptitude · Geometry · easy

Answer: 60 parallelograms — Option C

1. Choose 2 lines from Set 1 (4 parallel lines): C(4,2) = 4!/(2! × 2!) = 6
2. Choose 2 lines from Set 2 (5 parallel lines): C(5,2) = 5!/(2! × 3!) = 10
3. Total parallelograms by multiplication principle: total = 6 × 10 = 60