Parallel segment in a triangle and area of the lower trapezium:\nPoints P on AB and Q on AC satisfy PQ ∥ BC. If AP:PB = 2:3 and area(ΔAPQ) = 8 sq cm, find the area of trapezium PQCB.

Difficulty: Medium

Correct Answer: 42 sq cm

Explanation:


Introduction / Context:
A segment parallel to the base of a triangle creates a smaller similar triangle at the top. Areas scale with the square of the linear ratio. We use the given small-triangle area to recover the full triangle’s area, then subtract.


Given Data / Assumptions:

  • P on AB, Q on AC, PQ ∥ BC.
  • AP:PB = 2:3 → AP/AB = 2/5.
  • Area(ΔAPQ) = 8 sq cm.


Concept / Approach:
ΔAPQ ~ ΔABC with linear ratio 2/5. Therefore, area(APQ) : area(ABC) = (2/5)^2 = 4/25.


Step-by-Step Solution:

area(ABC) = area(APQ) * (25/4) = 8 * (25/4) = 50 sq cm.Area(trapezium PQCB) = area(ABC) − area(APQ) = 50 − 8 = 42 sq cm.


Verification / Alternative check:
Proportional reasoning aligns with standard results from the Basic Proportionality Theorem / similarity of triangles.


Why Other Options Are Wrong:
50 is the whole triangle; 18 and 14 are too small; 32 does not match the derived difference.


Common Pitfalls:
Using linear ratio directly on area (forgetting the square), or misreading AP:PB as AP:AB.


Final Answer:
42 sq cm

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