A chess board contains 64 equal squares and the area of each square is 6.25 cm2. A border round the board is 2 cm wide. Find the length of the side of the chess board.
Let the length of the side of the chess board be x cm. Then,
Area of 64 squares = (x−4)2
Therefore,
(x−4)2=64×6.25
x2−8x+16=400
x2−8x−384=0
x2−24x+16x−384=0
(x−24)(x+16)=0
x=24 cm