First, we should figure out how many ounces the bolts the carpenter purchased weighs. There are 16 ounces in a pound, therefore we should multiply this number by the number of pounds (3).
16*3= 48 ounces
Each bolt weighs 1/15 an ounce. Therefore, to find the number of bolts that the carpenter bought, we should total weight of bolts (48 ounces) by the weight of each bolt (1/15).
48 / 1/15 = 720
The carpenter bought 720 bolts.