There is 50% first year allowance which brings the written down value to 400M
Then it is 40% reducing balance, so 160 (40% x 400) the following year, bring it down to 240. 96 (40% x 240) the following year, bringing it down to 144. 57.6 (40% x 144) the following year,bringing it down to 86.4. 34.6 (40% x 86.4) the following year, bringing it down to 51.8.