Question : In measuring the sides of a rectangle, there is an excess of $5\%$ on one side and $2\%$ deficit on the other. Then the error percentage in the area is:
Option 1: $3.3\%$
Option 2: $3\%$
Option 3: $2.9\%$
Option 4: $2.7\%$
Correct Answer: $2.9\%$
Solution :
Let the original sides be $\mathrm{a}$ and $\mathrm{b}$.
Initial area, $\mathrm{A_\text{initial}=ab}$
There is an excess of $5\%$ on one side.
The new length of this side $=\mathrm{1.05a}$
There is a deficit of $2\%$ on the other side.
The new length of this side $=\mathrm{0.98b}$
Final area, $\mathrm{A_\text{final}=1.05a \times 0.98b = 1.029ab}$
The percentage change in the area $=\mathrm{\frac{A_\text{final} - A_\text{initial}}{A_\text{initial}} \times 100}$
The percentage change in the area $= \mathrm{\frac{1.029ab - ab}{ab} \times 100 = 2.9\%}$
Hence, the correct answer is $2.9\%$.
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