A workshop buys drive belting by the metre. The purchase clerk argues that the belting offered by a second supplier is the better buy for the workshop, because it is priced at 210 rupees a metre against the 260 rupees a metre paid for the belting now in use. Which of the following is an assumption on which the clerk's argument depends?

The clerk's evidence is a price for each metre bought while the claim is about what the workshop spends, and the two meet only through how long a metre lasts. Belting at 210 rupees that wears out in half the time costs more over a year than belting at 260, and the argument collapses. Carriage, growing consumption and colour do nothing to join the price to the running cost.