> This site says theer are about 160 seeds per pound
Well, it also says that "A pound of sunflower seeds weighs approximately 1/3 of an ounce (10 grams)" and "The average price per pound for sunflower seeds is 1,260" [sic: no units]. So you'll forgive me if I approach its other claims with a modicum of suspicion.
actually since a pound is around 450 grams, that would be 3 grams per seed, not 0.3 grams. So the 50 milligrams is off by almost 2 orders of magnitude.
Is think the estimation is almost correct, but it has a bad calculation
920/0.02 = 46,000,000 (but the actual result is 46,000)