Question: Trey is hanging wall decorations around his house. He uses a nail for each of two-thirds of them, a thumbtack for each of two-fifths of the rest, and a sticky strip for each of the other decorations. He used 15 sticky strips. How many nails did Trey use? Think carefully first, then make a decision:
Trey used 15 sticky strips for 3 / 5 of the remaining decorations after using nails, so he used 15 *  / 3 / 5 = 25 thumbtacks and sticky strips. The 25 decorations were 1 / 3 of the total decorations, so he used 25 / 1 / 3 = 75 total decorations. The nails were 2 / 3 of the decorations, so Trey used 75 decorations * 2 / 3 = 50 nails. So the answer is 50.