Question

each side of rectangular polygon is 2.5cm in length .the perimeter of the polygon is 12.5cm.how many sides does the polygon have

Answer 1

There are 5 sides (a pentagon). The perimeter is the length of one side times the number of sides.

Regular polygon has same length for all sides.
therefore 
no.of sides × length of each side = perimeter
n(2.5)=12.5
n=12.5/2.5
n=5
therefore no.of sides = 5