Question

length : 20 mm Breadth : ? perimeter: 50 mm​

Answer 1

$length = 20mm$

$perimeter = 50mm$

$p = 2(l + b)$

$50 = 2(20 + b)$

$\cancel \frac{50}{2} = 20 + b$

$b = 25 - 20$

$b = 5$

$\therefore \: b = 5mm$

Answer 2

$length = 20mm$

$perimeter = 50mm$

$p = 2(l + b)$

$50 = 2(20 + b)$

$\cancel \frac{50}{2} = 20 + b$

$b = 25 - 20$

$b = 5$

$\therefore \: b = 5mm$