SOLUTION: brian's average mark on three tests was 78. the mark on his first test was 86 his second test was three more than his third. what mark did he get on the second and third test

Question 846871: brian's average mark on three tests was 78. the mark on his first test was 86 his second test was three more than his third. what mark did he get on the second and third test
Answer by josh_jordan(263) (Show Source): You can put this solution on YOUR website!
To solve, we need to know how to compute an average so we can correctly set up the equation. An average is computed by added each number in a group together and then dividing that result by the total of numbers that were added together. Let's look at what we know:

Average on 3 Tests: 78
Mark on First Test: 86
Mark on Second Test: x
Mark on Third Test: y

We are told that the mark on the second test was 3 more than the mark on the 3rd test. So, we can change the Mark on Second Test to read as: y + 3:

Average on 3 Tests: 78
Mark on First Test: 86
Mark on Second Test: y + 3
Mark on Third Test: y

Now, we can set this up as an equation, based on how we compute an average of a group of numbers:

Next, add everything in the numerator of the fraction on the left side of the equation, which gives us:

Next, we need to get the y all by itself on the left side of the equal sign. To do this, we can first multiply both sides of the equation by 3, which gives us:

----->

Next, subtract 89 from both sides of the equation:

----->

Then, divide both sides by 2:

----->

We have just figured out what the 3rd test score is. To find out the second test score, which we are told is 3 more than the 3rd test score, we will add 3 to 72.5, giving us 75.5.

Therefore Brian got a 75.5 and 72.5 on his second and third tests, respectively.
RELATED QUESTIONS
Deon's average mark for his first two spelling tests is 10.After the third test,his... (answered by rothauserc)

jackie's average mark on her 3 tests was 78.the makrk on test one was 86. her averge mark (answered by josmiceli)

conner average grade on three math test are 93 on his first test it was a 98 and on his... (answered by JBarnum)

Justin has an average score of 83 on three tests. His average score on the first two... (answered by Fombitz)

sophie's average mark on 3 tests was 80.the mark on the first test was 76. her average... (answered by lwsshak3)

Gary earned 78%, 83% and 90% percent on his first three tests. What percent do you need... (answered by vheroli)

Juan's score on his second test was 87. This was 14 points more than his score on the... (answered by Alan3354)

Paul's second test score was 8 points higher than his first test score. His third score... (answered by CubeyThePenguin)

Mark had 14 problems wrong on his test. His score was 72% correct. How many problems were (answered by Theo)