A rectangular paper of 20 cm × 8 cm is folded 3 times. Each fold is made along the line of symmetry, which is perpendicular to its long edge. The perimeter of the final folded sheet (in cm) is
Options:
(A) 18
(B) 24
(C) 20
(D) 21
Official Answer Key:
A
Step-by-Step Solution & Explanation
The critical point is that the long edge is re-identified after every fold — the fold line is always perpendicular to whichever edge is currently longer, so that edge gets halved.
Fold 1: sheet is 20 × 8; long edge = 20 ⇒ halve it → 10 × 8
Fold 2: sheet is 10 × 8; long edge = 10 ⇒ halve it → 5 × 8
Fold 3: sheet is 5 × 8; long edge is now 8 ⇒ halve it → 5 × 4
Perimeter = 2(5 + 4) = 18 cm
Trap: always halving the original 20 cm side gives 20 → 10 → 5 → 2.5, i.e. a 2.5 × 8 sheet of perimeter 21 cm — option (D).
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