Your final grade is based on your overall percentage. We add up all points from homeworks and exams, and convert that to a percentage. At the end of the semester, we add up to 3% of extra credit. Grade cutoffs are listed farther down.
Homework assignments make up 38% of your score, exams 62%.
The grade cutoffs are fixed. There is no rounding up involved in computing the scores. If you have 79.99%, that is not an 80%.
# 
Assignment 
points each 
points total 
% each 
% total 

12 
Homework 
40 
480 
2.7% 
32.0% 

2 
Excel Homework 
15 
30 
1.0% 
2.0% 

4 
Practice exam 
10 
40 
0.7% 
2.7% 

1 
Practice Final 
20 
20 
1.3% 
1.3% 

HW Total  570 
38.0% 

1  Quiz  30 
30 
2% 
2% 

4 
Exam 
150 
600 
10.0% 
40.0% 

1 
Final Exam 
300 
300 
20.0% 
20.0% 

Quiz/Exam Total 
930 
62.0% 

1 
complete all HW* with 80%+ score 
1.0% 
1.0% 

1 
complete all Exams** with 50%+ score 
1.0% 
1.0% 

1 
Attend Lab session at lest once a week 
1.0% 
1.0% 

Extra Credit 
3.0% 

Course Total 
1500 
103.0% 
* Not including the practice exams. ** Not including the quiz.

In a class of 20 or 30 students, most instructors look for a reasonable gap as a grade cutoff. If three students have scores of 81%, 89%, 90%, the instructor would most likely put the cutoff for an A or A at 89% instead of 90%. However, Math 150 has anywhere from 600 to over 1000 students. There are no gaps in the scores. There will always be someone just a fraction of a percent below the cutoff. If we move one person up to the next category, the next person below them will come and ask. We don't move the cutoffs! Also, there is no rounding up involved in computing the scores. If you have 79.99%, that is a B, not a B. The only way to move up is to earn more points. It is better to do your best from the begining of the semester, not only Finals week. During the dead week your options are limited, but HW 11 and the final exam are still open. You may redo one of them to get a few extra points if you still have chance. The week before there is also Exam 4 still open. The registrar's current rules say that we have to give straight Ds for midterm grades, and then we cannot give D+/D/D for final grades. We are not set up for two different grading systems. If and when the registrar switches to the D+/D/D scheme for all grades, we will switch. 
MyMathLab has a tool labeled Overall Score, but it was so misleading that we disabled it (It doesn't count your missed assignments and exam in the total). Download a Math 150 Grade Estimator spreadsheet, and enter your scores (the scores for the practice exams are what you actually get). That will give you your actual current grade. Your midterm and final grades will be based on the same calculations.