It takes 200 pieces to pave the floor with 30 cm long square bricks on one side. If you use 20 cm long square bricks on the other side, how many pieces do you need

It takes 200 pieces to pave the floor with 30 cm long square bricks on one side. If you use 20 cm long square bricks on the other side, how many pieces do you need

90 times 200 = x times 40, 40x = 18000, x = 18000 divided by 40x = 450