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Question

If in triangle ABC, $DE \parallel BC$ and $AD/DB = \frac{1}{2}$, and $AE = 5\text{ cm}$, then $EC$ is:

This question was previously asked in
SSC CGL 2025 Tier 1 Question Paper (25-Sep-2025) (Shift 3)
The correct answer is
$10\text{ cm}$

Applying the Basic Proportionality Theorem

The problem involves a triangle ABC where a line segment DE is drawn parallel to the base BC, intersecting sides AB and AC at points D and E respectively. This setup allows us to use the Basic Proportionality Theorem (BPT), also known as Thales's Theorem.

Basic Proportionality Theorem (BPT)

The theorem states that if a line is drawn parallel to one side of a triangle intersecting the other two sides, then it divides the two sides proportionally. For triangle ABC with $DE \parallel BC$, the theorem gives us the following relationship:

$ \frac{AD}{DB} = \frac{AE}{EC} $

Calculation Steps

  1. Identify Given Values:
    • Ratio of segments on side AB: $AD/DB = 1/2$
    • Length of segment AE on side AC: $AE = 5\text{ cm}$
  2. Apply the BPT Formula: Substitute the known values into the BPT equation: $ \frac{1}{2} = \frac{5\text{ cm}}{EC} $
  3. Solve for EC: Rearrange the equation to solve for the unknown length, EC. $ EC = 2 \times 5\text{ cm} $ $ EC = 10\text{ cm} $

Therefore, the length of EC is $10\text{ cm}$.

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Important Questions from Triangles, Congruence and Similarity

  1. Angle between the internal bisectors of two angles ∠B and ∠C of a ΔABC is 132°, then the value of ∠A is

  2. In ΔPQR, PQ = PR and S is a point on QR such that ∠PSQ = 96° + ∠QPS and ∠QPR = 132°. What is the measure of ∠PSR?

  3. In Δ ABC, ∠A = 50°. If the bisectors of the angle B and angle C, meet at a point O, then ∠BOC is equal to:

  4. Triangle ABC is right angled at B. BD is an altitude intersecting AC at D. If AC = 9 cm and CD = 3 cm. then find the measure of AB (in cm).

  5. The base and altitude of an isosceles triangle are 10 cm and 12 cm respectively. Then the length of each equal side is:

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