posted by Bill .
Person weighing 650N lies on a bed of nails,each nail has area of 1m2 Assume 4Nm^-2 pressure is painful what is the smallest number of nails they could lay on and not be hurt
First, it's "lie" not "lay"
Next, surely a nail does not have an area of 1m^2.
Anyway, when you get a correct value for the area of a nail, say "a" m^2, just divide the weight by the number of nail areas, for n nails:
650N/(n*a) <= 4
n >= 162.5/a