Final answer:
The average of four numbers is calculated by adding all numbers together and dividing by four. The missing number 'x' can be found with the equation x = 4A - 58, where A is the given average. When A is known, substituting it into the equation will provide the value of the missing number.
Step-by-step explanation:
The question asks us to find the missing number when the average of four numbers is given, and three of the numbers are known: 12, 18, and 28. To calculate the average of these numbers, we add them up and divide by the total number of numbers, which in this case is four. Let's call the missing number 'x'. So the average (mean) is calculated as follows:
• Add the known numbers and the missing number: 12 + 18 + 28 + x.
• Divide the sum by 4 as there are four numbers.
• Set this equal to the given average and solve for x.
Let's assume the average is A (since it is not provided in the question), the equation becomes:
(12 + 18 + 28 + x) / 4 = A
Multiplying both sides by 4 to isolate x gives us:
12 + 18 + 28 + x = 4A
Adding the known numbers together:
58 + x = 4A
Finally, solving for x by subtracting 58 from both sides:
x = 4A - 58
With this equation, once the average A is known, we can determine the missing number x.