Question 703887
I would calculate it as
{{{97*0.9+80*0.1=95.3}}}
You multiply the 97 average before the final times its 90% value (0.90 as a decimal),
multiply the 80 final exam grade times its 10% value (0.10 as a decimal),
and add them.
 
For my son, I always calculated the individual value of each assignment in grade points, so he would know how to prioritize different assignments.
If he had had a 97 average in geometry going into the final, but had pending overdue English work, I would calculate that the geometry final could get him from
{{{97*0.9+0*0.1=87.3}}} to {{{97*0.9+100*0.1=97.3}}},
so the pending English work that his passing depended on was a much higher priority that the geometry final that could at most make the difference between a B and an A.
In the same way, at any time during the school year, completing some assignment that got him 1 or 2 points in the final grade could be shrugged, as long as he did not do that too often.