back-of-the-envelope calculation meaning in Chinese

封底计算

To see what subjects they addressed and in what proportions . the results of my informal , back - of - the - envelope calculations were rather disheartening
根据我非正式的统计结果，我在信封背面所计算出的统计数值令人相当失望。
Back - of - the - envelope calculations from goldman sachs suggest that if banks suffer a $ 200 billion loss on subprime mortgages but want to keep their capital ratios at an average level of 10 % , that would stifle lending by a whopping $ 2 trillion
从高盛粗略的计算可以看出如果银行由于次级贷而产生2000亿美元的损失，但是还想让他们的资本充足率保持在10 %这个水平线上，那么就不得不削减2万亿美元的巨额借贷。
And a back - of - the - envelope calculation based on the 1 . 8m sorts of organism recognised so far as species under the linnaean system , on the rate at which new species are being discovered and on such ecological matters as the average number of parasites ( themselves new species ) that each free - living species harbours , suggests the final total may be around 30m
一个以三部分，即：在林耐分类系统中迄今为止被认定是物种的180万种微生物、新物种的发现速率和诸如在每个独立生存的物种中藏匿的平均寄生虫数量（它们本身也属于新物种）等生态因素，为基础的估算表明全球物种的总数是在三百万左右。