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Question

Ajay can do a painting in 12 days. Amit is 70% more efficient than Ajay. What is the number of days Amit would need to finish the same painting?

This question was previously asked in
RRB ALP 2018 CBT 2 Fitter Question Paper (21-Jan-2019) (Shift 3)
The correct answer is
$7 \frac{1}{17}$

Work and Time: Calculating Amit's Painting Duration

This problem involves calculating the time taken by an individual based on relative efficiency compared to another person.

Understanding Efficiency and Time

Efficiency and the time taken to complete a task are inversely proportional. If someone is more efficient, they will take less time to finish the same job.

  • Let the efficiency of Ajay be $E_A$.
  • Let the efficiency of Amit be $E_M$.
  • Let the time taken by Ajay be $T_A = 12$ days.
  • Let the time taken by Amit be $T_M$.

Calculating Amit's Efficiency

Amit is 70% more efficient than Ajay. This means Amit's efficiency is Ajay's efficiency plus 70% of Ajay's efficiency.

Mathematically:

$E_M = E_A + (70\% \times E_A)$ $E_M = E_A + (0.70 \times E_A)$ $E_M = 1.70 \times E_A$

Calculating Amit's Time

Since time is inversely proportional to efficiency ($T \propto \frac{1}{E}$), we can set up the ratio:

$\frac{T_M}{T_A} = \frac{E_A}{E_M}$

Substitute the known values and the relationship between $E_M$ and $E_A$:

$\frac{T_M}{12 \text{ days}} = \frac{E_A}{1.70 \times E_A}$ $\frac{T_M}{12} = \frac{1}{1.70}$

Now, solve for $T_M$:

$T_M = 12 \times \frac{1}{1.7}$ $T_M = \frac{12}{1.7}$

To simplify, multiply the numerator and denominator by 10:

$T_M = \frac{120}{17}$

Convert the improper fraction to a mixed number:

$120 \div 17 = 7$ with a remainder of $1$. $T_M = 7 \frac{1}{17}$ days.

Conclusion

Amit would need $7 \frac{1}{17}$ days to finish the same painting.

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