National Australia Bank has reported an unaudited statutory net profit of A$1.65 billion for the quarter to 31 December 2017. Cash earnings, also unaudited and also reported as $1.65 billion, declined during the quarter but the result represented a three per cent increase in cash earnings growth compared to the comparable quarter in the previous financial year.Revenue was up by one per cent, with good growth in business and private banking, and corporate and institutional banking revenue.Net interest margin declined but, excluding markets and Treasury impacts, was broadly stable, the bank levy and competitive pressures in home lending notwithstanding.NAB's chief executive officer, Andrew Thorburn, said: "We are on track to deliver the targets announced with the financial year 2016/17 results, including an estimated $1.5 billion increase in investment by the end of financial year 2020. Cost savings of more than $1 billion continue to be targeted by the end [of that same year]."Expenses rose four per cent due to higher investment spend and personnel costs, including enterprise bargaining agreement increases.Thorburn said he expected expenses to grow five to eight per cent in the current financial year 2017/18, then to remain broadly flat over the 2018/19 to 2019/20 financial years.More of NAB's small business customers have access to faster and simpler unsecured credit with QuickBiz loans limits increasing from $50,000 to $100,000. Approximately one-third of all NAB's new business lending for small business customers are written by QuickBiz.Customers can expect more "voice enabled personalised banking information" through Amazon Alexa and Google Assistant as the bank looks to double its investment in NAB Labs over FY 18.In reporting asset quality, NAB stated bad and doubtful debts charges fell 23 per cent to $160 million. Some reasons included the "non-repeat of collective provision overlays raised in the second part of FY17, combined with lower specific charges, partly offset by collective provision increases for plan mortgage model changes".Asset quality improved with the ratio of 90+ days past due and gross impaired assets to gross loans and acceptances down three basis points to nought .67 per cent, benefiting mainly from continued improvement conditions for New Zealand dairy customers.Among NAB's key ratios, as at 31 December 2017: Group Common Equity Tier 1 ratio of 10.2 per cent, with the increase in September 2017 benefiting from lower risk-weighted assets and the 1.5 per cent dividend reinvestment plan discount for the FY 17 final dividend; NAB expects to meet APRA's "unquestionably strong" target of 10.5 per cent in an orderly manner by January 2020; leverage ratio (APRA basis) of 5.4 per cent; liquidity coverage ratio quarterly average of 126 per cent; andnet stable funding ratio of 110 per cent.