You are in Pakistan and do not have access to the web. You are sampling a strath terrace above the Indus in its Middle Gorge near Nanga Parbat, and need to know how large a sample to collect. You cannot simply say “I don’t know” and take a sample the size of your vehicle, because 1) there is limited space in the vehicle, and 2) it costs money to ship the samples home. You are 200 m above the river at an elevation of 3700 m. The rock you are sampling appears to be a highly metamorphosed granite. List all assumptions you are making in the calculation.