Brittany got a 78 on her first test. After her second test, her average rose to an 81. What grade did she get on her second test? Let's think first. Chain of thought:
First multiply her average grade by the number of tests she took to find the total number of points she scored: 81 points * 2 = 162 points. Then subtract the number of points she scored on her first exam to find how many points she scored on her second exam: 162 points - 78 points = 84 points.
Therefore, the answer is 84.