The true discount on a bill due 9 months hence at 16% per annum is ₹ 189. The amount of the bill is
Aptitude
True Discount
Difficulty: Medium
Choose an option
-
A₹ 1386
-
B₹ 1764
-
C₹ 1575
-
D₹ 2268
Answer
Correct Answer: ₹ 1764
Explanation
### Concept & Formula
To find the total amount of the bill, compute the present worth from the true discount and add them together.
$$ \text{PW} = \frac{100 \times \text{TD}}{R \times T} $$
$$ \text{Amount} = \text{PW} + \text{TD} $$
### Step-by-Step Solution
- Given True Discount (TD) = ₹ 189
- Rate (R) = 16%
- Time (T) = 9 months = $\frac{9}{12}$ years = $\frac{3}{4}$ years
- Find the Present Worth (PW):
$$ \text{PW} = \frac{100 \times 189}{16 \times (\frac{3}{4})} $$
$$ \text{PW} = \frac{18900}{12} = 1575 $$
- Calculate the Amount:
$$ \text{Amount} = 1575 + 189 = 1764 $$
### Exam Strategy & Shortcut
Using the direct relationship for Amount:
$$ \text{Amount} = \text{TD} \times \frac{100 + (R \times T)}{R \times T} $$
$$ \text{Amount} = 189 \times \frac{100 + 12}{12} = 189 \times \frac{112}{12} $$
Cancel common terms: $189 \times (\frac{28}{3}) = 63 \times 28 = 1764$. This saves calculating the intermediate PW step.
### Common Pitfall
Selecting option (c) ₹ 1575, which is merely the present worth, rather than the final amount of the bill.
### Final Answer
Therefore, the correct answer is **₹ 1764**.