Question

The average of 5 quiz grades is 10. When the lowest grade is dropped and the new average is calculated, it turns out to be 11. What was the score of the dropped grade?

Answer 1

The score of the dropped grade is 6

Explanation:

To find the average of a set of numbers you need to add all the numbers and divide by how many numbers there are. The problem wants you to solve it in reverse. Let put this into an algebraic equation with a, b, c, d, and e being the variables of the test scores

(a+b+c+d+e)/5=10

Then we can multiply both sides by 5 and get

a+b+c+d+e=50

Lets assume that c is the lowest test score. To calculate the average of that we get

a+b+d+e/4=11

Doing the same thing, we know that a+b+d+e=44

Now compare the two:

a+b+c+d+e=50

a+b+d+e=44

We can now know that c=50-44=6

So, 6 is the score of the dropped quiz. Hope that helped!