Question

If the length of a rectangle increased by $20\%$ and the breadth of the rectangle decreases by $10\%$, then find the $\%$ change in area

• A. increase $5\%$
• B. increase $8\%$
• C. decrease $5\%$
• D. decrease $8\%$

Answer 1

The correct option is B increase $8\%$

$l^1=l+\left(\frac{20}{100}\right)l=1.2l$

$b^1=b-\left(\frac{10}{100}\right)b=0.9b$

$\Rightarrow A^1=l^1{b}^1=\left(1.2\right)\left(0.9\right)lb$

$=1.08A$

$\therefore \uparrow$ in area $=\left(\frac{A^1-A}{A}\right)\times 100$

$=8\%$