This part of question 1 asked for a calculation of net present value (NPV). Many answers scored full marks here. Some answers lost marks because they left something out (error of omission). These answers, for example, did not include incremental fixed costs, or working capital investment, or working capital recovery, or scrap value, or even in some cases one whole year of income and costs (the evaluation was over five years).

Other answers lost marks because there was a mistake in the way that NPV was calculated (error of principle). Such mistakes included treating working capital recovery or scrap value as tax-allowable deductions, and calculated tax liability on sales or on contribution, rather than on net taxable cash flow.