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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 2 Paper 1 Question Paper (19-Jan-2026)
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. The radius of the circumcircle of an equilateral triangle of √3 unit side, is:

  2. If the ratio of the angles of a triangle is 3 : 5 : 7, find the value of the largest angle.

    A. 36°

    B. 60°

    C. 84°

    D. 15°

  3. If ΔABC and Δ PQR are similar and \(\rm\frac{BC}{QR} = \frac{1}{3}\) , find  \(\rm\frac{ar(\Delta PQR)} {ar(\Delta BCA)}\)

  4. If the angles of a triangle are in the ratio of 2 : 5 : 8, then find the value of the smallest angle.

  5. ABCD is a parallelogram. Side BC is produced to E such that BC = CE. Join AE which intersects side CD at P. The area of triangle ABE is:

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