Elizabeth Mullane (right) describes her group’s project to Jerry Ing ’04 (left) at the MIT/Cambridge Science Expo in Johnson Ice Rink on Tuesday afternoon. Mullane’s group, seventh grade students from M. E. Fitzgerald School, aimed to build a cardboard box oven that heats evenly. They found that brownies baked perfectly in their oven when warmed by two 100 watt bulbs for 50 minutes.