Jack needs to earn a C. His test scores are 67, 72, 81, and 75. His final exam will count as three test scores. To earn a C, Jack's average must lie between 70 and 79(inclusive). What test score range can Jack earn on his final exam to receive a C?

Question

anonymous · Answer

Let x = the required test score on the exam
:
Exam is worth 3 scores (3x), therefore we will be dealing with total of 7 test scores
:
 (3x+67+72+81+75)/7= 70, his minimum for a C average
 (3x+295)/7= 70
Multiply both sides by 7
3x + 295 = 7(70)
3x + 295 = 490
3x = 490 - 295

3x = 195
x = 195/3 
x = 65 min score on the exam for have a 70 average
:
Do the same with to find test score for 79 average
(3x+67+72+81+75)/7 = 79, his minimum for a C average
 (3x+295)/7= 79
Multiply both sides by 7
3x + 295 = 7(79)
3x + 295 = 553
3x = 553 - 295
3x = 258
x = 258/3
x = 86 score on the exam for have a 79 average
:
The range of test scores would be from 65 to 86 for a 70 to 79 average .

anonymous · Answer

thanks.