Reuben has scores of 70, 75, 83 and 80 on four Science quizzes. What score must he get on the next quiz to achive an average of at least 80.

Question

I just want the answer to make my homework and to understand this really complicated topic in math and have good grades.

Answer 1

Hi Maria, the way to work these types of problems is to remember how to find an average. To find the average you sum the individual elements and then divide by the total number of elements.

 

Here you are given 4 elements, 70, 75, 83, and 80. The fifth element (the score on the next quiz) is represented by x.

 

We know the sum of the 4 elements plus x when divided by 5 will equal 80.

 

Equation:

 

(70 + 75 + 83 + 80 + x) / 5 = 80

 

( 308 + x) / 5 = 80

 

Multiply both sides by 5:

 

308 + x = 400

 

Subtract 308 from both sides:

 

x = 92

 

Reuben will have to score 92 on the next quiz to have an average of 80.

 

Questions?

Answer 2

In order to calculate the average, you must add up the total, and then divide by the number of data used.

 

In this example, we know four of Reuben's scores, but we want to calculate his fifth. In other words, the average can be calculated as follows:

 

(70 + 75 + 83 + 80 + x) / 5

(x + 308) / 5

 

where x is the unknown score.

 

We want the average score to equal 80, so let's set the equation equal to 80

 

(x + 308) / 5 = 80

x + 308 = 400

x = 92