Harry had grades of 70,80,85 and 80 on his quizzers. If all quizzers have the same wight, what grade must he get on his next quiz so that his average will be 80?

Options

A. 85
B. 90
C. 95
D. 100

Explanation

To find out what grade Harry needs on his next quiz to achieve an average of 80, we can follow these steps:

### Step 1: Calculate the total of Harry's current grades
Harry's current grades are 70, 80, 85, and 80. We first need to sum these grades.

\[ \text{Total of current grades} = 70 + 80 + 85 + 80 \]

### Step 2: Perform the addition
Now, let's calculate the total:

\[ 70 + 80 = 150 \]
\[ 150 + 85 = 235 \]
\[ 235 + 80 = 315 \]

So, the total of Harry's current grades is 315.

### Step 3: Set up the equation for the average
Let \( X \) be the grade Harry needs on his next quiz. The average of all five quizzes should equal 80. The formula for the average is:

\[ \text{Average} = \frac{\text{Total of grades}}{\text{Number of quizzes}} \]

For Harry, this becomes:

\[ 80 = \frac{315 + X}{5} \]

### Step 4: Multiply both sides by 5
To eliminate the fraction, multiply both sides of the equation by 5:

\[ 400 = 315 + X \]

### Step 5: Solve for \( X \)
Now, we need to isolate \( X \):

\[ X = 400 - 315 \]
\[ X = 85 \]

### Conclusion
Harry needs to score **85** on his next quiz to achieve an average of 80.

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