John averaged 82 out of 100 on his first three tests. What was John’s score on the fourth test if his average after the fourth test dropped to 79 out of 100?
a) Cannot be found b) 80 c) 75 d) 70
Can somebody please help me with this question, i know the right answer is 70 but what i don't know is how to do it.
Please help ASAP.

An average is a single number that represents a collection of numbers, often the sum of the numbers divided by the number of numbers in the collection.

Let the sum of the scores in the first three tests be 'x'.

Given that the average John's score in the first three tests is 82, therefore, the average can be written as,

[tex]\rm Average = \dfrac{\text{Sum of the first three test}}{3}[/tex]

[tex]82 = \dfrac{x}{3}\\\\x = 82 \times 3 = 246[/tex]

Now, let the sum of the scores in the four tests be 'y'.

As we know the sum of the scores of the first three tests is 246, and the average score dropped to 79 during the fourth test, therefore,

[tex]\rm Average = \dfrac{\text{Sum of the four test}}{4}[/tex]

[tex]79 = \dfrac{y}{4}\\\\y = 79\times 4 = 316[/tex]

Further, the score of the fourth test is the difference between the sum of the four tests and the sum of the scores in the first three tests. Therefore,

[tex]\text{Socre in the fouth test} = y-x = 316-246 = 70[/tex]

Hence, the score of the fourth test is 70.

Learn more about Averages:

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