My grade is 88.6% (High B) and we get 80%(Assessment Grade) and 10%(Homework). My teacher is now making this 70%(Assessment Grade) and 30%(Homework). I have done all my homework 100% and I've been doing bad in assessments lately.
Will my grade reach that 90% mark? This grade will go up to a 88.9 at the least.(test retakes)
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If you are going from a grade of 88.6% with an $x$ in Assessments and $100$ in Homework, and shifting the percentages from $80/20$ to $70/30$ your grade will be a 90.025
You previously were getting $20$ percentage points from homework, which will go up to 30. And you were getting $68.6$ percentage points from assessment, which will go to $68.6\times\frac{.7}{.8}=60.025$
Currently, you have $.8 A + .2 H = 0.886$, where $A$ is your assessment grade and $H$ is your homework grade. Since your homework grade is 100%, let $H = 1$. Solve for $A$:
$$A = \frac{.886-.2}{.8} = .8575.$$
Now, plug these scores into the modified formula:
$$.7 (.8575) + .3 (1) = .90025.$$
Your score will therefore be just above 90%.