Given 3 scores of 74, 78, 63:
what should be score number 4
in order to attain an average score of 80?
Setup Average Equation:
| Average = | Sum of our 3 numbers + unknown score of x |
| Total Numbers |
| 80 = | 74 + 78 + 63 + x |
| 4 |
Cross Multiply
74 + 78 + 63 + x = 80 x 4
x + 215 = 320
Subtract 215 from both sides of the equation to isolate x:
x + 215 - 215 = 320 - 215
Final Answer
x = 105
