Answer:
I know I am almost a year late! lol But I just learned about it so I figured I could still help!
Explanation:
The answer is 90.
Use this example/solution I was given to learn from:
Example:
Aaron's P.E. class is completing a unit on bowling. So every Friday afternoon for the last three weeks, they have bowled one game at a nearby bowling alley. His scores have been 121, 147, and 96. What would he have to bowl next time in order to have a mean score of 128?
Solution:
Let x represent Aaron's fourth and unknown score. To have a mean of 128, the sum of the four scores would have to be divided by 4. To get that sum by itself, multiply it by 4. You also have to multiply the desired mean of 128 by 4. So the sum of the four scores is equal to 128 times 4.
121 + 147 + 96 + x = 128 ∙ 4
• Substitute in the values of the four scores.
364 + x = 512
• Simplify.
364 - 364 + x = 512 - 364
• Subtract 364 from each side of the equation.
x = 148
• Simplify.
Aaron must score a 148 in order to have a mean score of 128.
(From Calvert Homeschool)