Question 986378
 So far this semester your test scores have been 75, 91, and 85.
 Set up and solve an equation for each problem.
:
a. If all of the tests are equally weighted, what score must you get on the fourth test to have a test average of 88? Define any variable used.
let a = the 4th test grade
{{{((75 + 91 + 85 + a))/4}}} = 88
multiply both sides by 4, add the grades
251 + a = 4(88)
a = 352 - 251
a = 101 to have an 88 average, (you may need extra credit here)
:
b. If the fourth test counts twice as much as the other three tests, then what score must you get on the fourth test to have a test average of 90? Define any variable used.
let b = test grade for this to be true,
Treat it like there are two grades of b, and average 5 tests
{{{((75 + 91 + 85 + 2b))/5}}} = 90
Multiply both sides by 5
251 + 2b = 5(90)
2b = 450 - 251
2b = 199
b = 199/2
b = 99.5 required to get a 90 average