Question

if the Length and width of a rectangle all increased by 10% and 20% respectively then how many percentage increase in the area of the rectangle

Answer 1

$let \: \: length \: \: be \: \: l \: \: and \: \: width \: \: be \: \: b \\ initial \: area = lb \\ \\ after \: \: increase \\ length \: becomes \: \: 1.1l \\ width \: \: becomes \: \: 1.2b \\ final \: area = 1.1l \times 1.2b = 1.32lb \\ \\ \% \: increase \: in \: area \\ = \frac{final \: area - initial \: area}{initial \: area} \times 100\\ = \frac{1.32lb - lb}{lb} \times 100 = 32\%$