Question

plz solve the problem.​

Answer 1

$\Large\text{\underline{\underline{Danger points}}}$

If we consider the increase and decrease in the length, the calculation may look as -

$\cdots\longrightarrow25\times\dfrac{12}{100}\times 15\times\dfrac{20}{100}.$

But, it is not correct. Keep this in mind.

$\Large\text{\underline{\underline{Explanation}}}$

The correct calculation of the new area is -

$\cdots\longrightarrow25\times(1+\dfrac{12}{100})\times 15\times(1-\dfrac{20}{100}).$

Calculating furthermore, -

$\text{ \cdots\longrightarrow\boxed{\begin{aligned}&25\times 15\times\dfrac{112}{100}\times\dfrac{80}{100}\\\\&=25\times15\times\dfrac{28}{25}\times\dfrac{4}{5}\\\\&=(25\times15)\times\dfrac{112}{125}\\\\&=(25\times15)\times\dfrac{896}{1000}\\\\&=(25\times15)\times(1-\dfrac{104}{1000}).\end{aligned}} }$

Now, the previous area is -

$\cdots\longrightarrow25\times15.$

Hence, the answer is -

$\text{ \cdots\longrightarrow\dfrac{104}{1000}=10.4\% decreased.}$