Answer:
The missing card's value is 4.
There are 3 cards with a summed value of 15.
Explanation:
The mean is the average of the numbers. This is determined by adding the numbers and then dividing by the number of numbers added.
Fot the information provided, let X stand for the missing number. The three numbers are 8, 3, and X. The average of these numbers is 5.
We can write the calculation for the average as:
(8 + 3 + X)/3 = 5 [the sum of the numbers divided by the number of numbers ,3)
Solve the resulting equation for X:
(8 + 3 + X)/3 = 5
(8 + 3 + X) = 15
11 + X = 15
X = 4
The missing number is 4.
The question "What is the total number of these cards" is ambiguous and has two legitimate answers:
1. The total number of cards is 3
2. The total value of the three cards is (8+3+4) = 15 {I suspect this answer the intended question]
CHECK:
Is the mean of 8, 3, and 4 equal to 5?
(8+3+4)/3 = 5?
(8+3+4)/3 = 5?
(15)/3 = 5 YES