Algebra Demystified 2nd Ed

Chapter 8 linear appliCaTionS 255

4. Let x represent Ava’s final exam grade. Her test average is (68 + 73 + 80
   
   
   • 95)/4 = 79. Then^13 test average + 31 presentation grade + 31 final exam
     grade is 80 becomes
   
   
   
   

1

3

79 1

3

75 1

3

80

79

3

25

3

80

379

3

25

3

()++() ()=.

++=

 ++



x

x

 x



=









++⋅=

++=

380

379

3

3253

3

240

79 75 240

()

() x

x

1154 240

154 154

86

+=

−−

=

x

x

Ava’s final exam grade needs to be 86 to obtain an average of 80.

5. Let x = sixth quiz grade. The course grade^45 quiz grade +^15 book report
   becomes

4
5

72 66 69 80 85

6

1

5

 +++++ 90







x + ().

Simplified, the above is

4
5

372

6

18 4372 4

30

18 1488 4

30

 + 18







xx+=()+ += + x+.

We want this quantity to equal 80.

1488 4

30

18 80

301488 4

30

18 30 80

30148

+ +=

 + +







=

x

x ()

884

30

 + 30 18 2400







x +=()