Given 4 scores of 78, 76, 82, 84:
what should be score number 5
in order to attain an average score of 90?
Setup Average Equation:
| Average = | Sum of our 4 numbers + unknown score of x |
| Total Numbers |
| 90 = | 78 + 76 + 82 + 84 + x |
| 5 |
Cross Multiply
78 + 76 + 82 + 84 + x = 90 x 5
x + 320 = 450
Subtract 320 from both sides of the equation to isolate x:
x + 320 - 320 = 450 - 320
Final Answer
x = 130
