Answer: The grade must be greater than or equal to 97
Explanation:
This is a question about averages. One determines averages by adding up all the original numbers (89 and 84) and dividing by the number of numbers (2). If we want to find out a third test grade that would get the grade up to a 90 we should use the formula for finding averages as an algebraic equation.
Set up the equation
89 + 84 + x/3 = 90
The x represents the third test grade, which is what we must solve for. The 89 and 84 were the two previous grades. And the 90 is what the average must be according to the question.
Solve the equation.
1. 89 + 84 + x/3 = 90
2. 89 + 84 + x = 270
3. 84 + x = 181
4. x = 97