Rebecca makes her own earrings out of buttons, magnets, and gemstones. For every earring, she uses two magnets, half as many buttons as magnets, and three times as many gemstones as buttons. If Rebecca wants to make 4 sets of earrings, how many gemstones will she need? Think carefully first, then make a decision:
Four sets of earrings is 2 * 4 = 8 earrings. Since for one earring, she uses two magnets, for eight earrings she uses 2 * 8 = 16 magnets. Since she uses half as many buttons as magnets, then for 8 earrings she would use 16 / 2 = 8 buttons. Since she uses three times as many gemstones as buttons, then in 8 earrings, she will use 8 * 3 = 24 gemstones. So, the answer is 24.