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In order to get a C in math, William must have an average score of 70 or more.
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His test scores so far are 63.3, 85, 79.73, and 70.57.
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Calculate the minimum score William needs to get on his final test to earn a C.
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First of all, we need to know what an average is.
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We find the average score by taking the sum of all values and dividing that by the number of values.
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William’s average in math will be the sum of all his test scores divided by the number of tests he took.
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And this average needs to be greater than or equal to 70 in order for him to get a C.
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So let’s fill in what we know.
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William’s first test, he scored a 63.3.
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On his second test, he scored 85; on his third test, 79.73; on his fourth test, 70.57.
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And we don’t know what he scored on his final.
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That’s what we’re trying to find.
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So we’ll just add plus 𝐹.
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How many tests did William take in math?
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He’s already taken four and he has one final test to take, for a total of five.
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And so we’ll divide by five.
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The first thing we can do is go ahead and add up his first four test results, which will give us 298.6.
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His final score will be added to this and then the average calculated by dividing by five.
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And we need this value to be greater than or equal to 70.
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So how do we go about finding 𝐹?
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Well, we can get the five out of the denominator by multiplying both sides of the equation by five.
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On the left side, the fives cancel out, leaving us with 298.6 plus 𝐹.
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And on the right side we have 70 times five, which is 350.
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Again, we’re trying to get 𝐹 by itself.
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And so we subtract 298.6 from both sides.
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The 298.6 cancels out on the left.
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And then we have 350 minus 298.6, which is 51.4.
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And what this inequality tells us is that 𝐹, the final score, must be greater than or equal to 51.4 in order for William to get a 70 in math.
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Our question has specifically asked the minimum score that William can get to earn a C in the class.
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The lowest score that William can earn on his final and still get a 70 in his class is 51.4.