Question

Julia received an 88, 90, 94, 89 on her first four English quizzes. What must she get on her fifth in order to have a 92 average?

Answer 1

99

Explanation:

You can set up a proportion, and solve for the variable (missing grade in this case):

`(88+90+94+89+x)/(5) =92`

Each grade is already in the database, so it can serve as the constant, and five is the denominator because to get a mean average, you must divide all the values by the number of values that exist. So, in this case, it would be 5, 4 including the missing grade, making it 5. Set the equation equal to 92, because that's her desired average, then just solve for x.

Multiply the 5 on both sides.

-> 5 cancels on left, and 5 multiplies with 92 to get 460.

`(5)(88+90+94+89+x)/(5) = 92(5)`

Add all constants on the left side of the equation.

-> 88+90+94+89=361

`361+x = 460`

Subtract that new constant (361) from the 460, and you get x=92.

-> 460-361=99

`x=99`

Hope this helped. :)