How to Find the Average | Math Review
We’re going to take a brief look at what an average is, and then take a look at a little bit more of a complicated word problem using average. You find average by adding all the numbers together, and then dividing that number by the amount of numbers you have.
Say we have the numbers 4, 5, and 9. We’re going to add those all together. Since we have three numbers we’re going to divide them by three. 4 plus 5 is 9, plus 9, equals 18, 18 divided by 3 equals 6. The average of these 3 numbers is 6.
Now, say that Kara is finishing up her semester and so she’s taking 4 tests so far. These are the grades she’s made 78, 82, 80, and 94. She wants her term average to be an 85. She wants to know on this last test how well does she have to do to get that 85.
We’re going to set up this problem so that we have term average equals 78, plus 82, plus 80, plus 94, plus X and then we have 5 numbers here. We’re going to count x as a number, so we divide it by 5. We have the test grades so far plus the test grade of this last test she has yet to take.
We know what term average she’s trying to get. We’re going to replace term average with an 85. The first thing we’re going to do is get rid of this denominator, multiply both sides by 5. We get 425 over here. Now we just need to add these numbers together, so we get 334 plus x.
Now it’s getting really simple, we just subtract 334 from both sides to get that X equals 91. There’s the answer to Kara’s question. Kara just needs to get a 91 on this last test to get a term average of 85. That’s how average works, and that’s how you can use average to figure out a word problem.