Terry has taken 4 of the 5 required tests for her math class. her grades are 83, 78, 64, and 91. terry wants to earn at least a "b" for the course. if 80 is the minimum b grade, what is the minimum score terry must get on her last test to get a b?

84

Step-by-step explanation:

Given, grades for first 4 tests are: 83, 78, 64, 91

Goal: To get an average of 80 points over 5 tests.

Let the score for the 5th test be x

Average score = total score for 5 tests ÷ 5 tests

(substituting the given values above),

80 = (83 + 78 + 64 +91 + x) ÷ 5

80 = (316 + x ) ÷ 5

(80)(5) = (316 + x)

400 = 316 + x

x = 400 - 316

x = 84

a

step-by-step explanation:

or

step-by-step explanation:

we need to solve for 'x' the following equation:  

we have that:

⇒

⇒ ⇒

factorizing, we get that:

  ⇒

then, the solutions are: or

nothing extraneous has been found!