When simplified, the product $\left(2 - \frac{1}{3}\right)\left(2 - \frac{3}{5}\right)\left(2 - \frac{5}{7}\right)\cdots\left(2 - \frac{997}{999}\right)$ is equal to
Aptitude
Simplification
Difficulty: Medium
Choose an option
-
A$\frac{5}{999}$
-
B$\frac{1001}{999}$
-
C$\frac{1}{1001}$
-
D$\frac{1001}{3}$
Answer
Correct Answer: $\frac{1001}{3}$
Explanation
### Concept & Formula
This problem contains a sequence where each term follows the pattern $\left(2 - \frac{2k-1}{2k+1}\right)$. Simplifying these fractions helps identify a telescoping behavior where terms eliminate each other diagonally.
### Step-by-Step Solution
Simplify each factor step-by-step:
$$2 - \frac{1}{3} = \frac{6 - 1}{3} = \frac{5}{3}$$
$$2 - \frac{3}{5} = \frac{10 - 3}{5} = \frac{7}{5}$$
$$2 - \frac{5}{7} = \frac{14 - 5}{7} = \frac{9}{7}$$
$$\vdots$$
$$2 - \frac{997}{999} = \frac{1998 - 997}{999} = \frac{1001}{999}$$
Write down the product with the newly simplified fractions:
$$\left(\frac{5}{3}\right) \times \left(\frac{7}{5}\right) \times \left(\frac{9}{7}\right) \times \cdots \times \left(\frac{1001}{999}\right)$$
Notice the cancellation trend: the numerator of the first term ($5$) cancels out with the denominator of the second term ($5$). The numerator of the second term ($7$) cancels out with the denominator of the third term ($7$), and this continues through the entire chain.
The surviving values are the first denominator ($3$) and the last numerator ($1001$):
$$\frac{1001}{3}$$
### Exam Strategy & Shortcut
Observe the first two terms: $\frac{5}{3} \times \frac{7}{5} = \frac{7}{3}$.
The result is always $\frac{\text{Last Numerator}}{\text{First Denominator}}$. Since the first denominator is $3$, look for options containing $3$ in the denominator or as a simplified fraction. Only option (d) matches this condition.
### Common Pitfall
Students often invert the final ratio, arriving incorrectly at $\frac{3}{1001}$ due to losing track of which part of the fraction cancels out at the start and end of the series.
### Final Answer
**Therefore, the correct answer is 1001/3.**