Question 519253
Your average is 83, so any score on a test that is less than 83 will bring your average down.  Similarly, any score higher than 83 will bring your average up.
.
A score of 73 will bring your average down.  A score of 73+5 = 78 likewise will bring your average down, but not as much as a 73 will.
.
As a general rule, never leave any points behind.  Counteracting the effects of 78 is easier than correcting a 73.
.
Consider students who fail to submit homework.  They usually get a 0 for doing so.  If they submitted a truly horrible homework, it is unlikely they would get a 0.  Consider an excellent student who skips an entire assignment vs. turning in half of it on time.
.
A (100 + 0) / 2 = 50, which is still a failing average.
A (100 + 50) /2 = 75, which may be passing average.
.
Plus, turning in half an assignment lends credibility to whatever reason there is for not being able to complete the assignment on time.