The 3 by 3 grid below shows nine 1cm×1 cm squares and uses 24 cm of wire. What length of wire is required for a similar 20 by 20 grid?

Question: The 3 by 3 grid below shows nine 1cm×1 cm squares and uses 24 cm of wire. What length of wire is required for a similar 20 by 20 grid?

Answer: The correct answer is 840 cms

A 20 by 20 grid used 21 lines of 20 cm in vertical and horizontal dimensions.

So, Answer = (21 + 21)20 = 42(20) = 840cms