PQRS is a square with side 20 cm. A, B, C, D are mid points of PQ, QR, RS and SP respectively.  Then perimeter of square ABCD is?

40\(\sqrt {2}\) cm

AB side of square ABCD is hypotheneus of triangle AQB's

⇒ AB = \(\sqrt {2}\) × AQ

        = 10\(\sqrt {2}\)                           [PQ = 20, so AQ = 10 cm]

Perimeter of square ABCD = 4 × side = 40\(\sqrt {2}\)