The true discount (TD) on a bill of ₹2160 is ₹360. Compute the banker’s discount (BD).

Difficulty: Medium

Correct Answer: Rs. 432

Explanation:


Introduction / Context:
True discount and face value are known; we must find BD. Use the identity TD = F * x / (1 + x) to find x, then use BD = F * x or BD = (1 + x) * TD. This avoids needing r or t individually.



Given Data / Assumptions:

  • F = ₹2160.
  • TD = ₹360.


Concept / Approach:
Let x = r * t. Then 360 = 2160 * x / (1 + x). Solve for x, then BD = 2160 * x.



Step-by-Step Solution:

360(1 + x) = 2160x ⇒ 360 = 2160x − 360x = 1800x ⇒ x = 0.2.BD = F * x = 2160 * 0.2 = ₹432.


Verification / Alternative check:
Also BD = (1 + x) * TD = 1.2 * 360 = ₹432, same result.



Why Other Options Are Wrong:
Values like 412, 422, 442 do not satisfy both TD and the derived x.



Common Pitfalls:
Using BD = TD / (1 + x) (incorrect direction); BD is larger than TD for x > 0.



Final Answer:
Rs. 432

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