Assume that in the balance sheet of a commercial bank, there are 450 billion yuan of deposits with the central bank, 40 billion yuan of cash assets, 300 billion yuan of legal reserves, and the total amount of deposits is 0.6 trillion yuan.

(1) Try to calculate the excess reserves and the proportion of excess reserves of the commercial bank. (Please keep two decimal places in the calculation results.)

(2) Please point out the limitations of judging bank liquidity by the ratio of excess reserves.