Answer:
We don't know exactly how much the post test is weighted.
If we assume that it's worth 20% of your grade, you would need to get approximately 91% on the test to raise your average to 70%:
We can set up an inequality to solve for this value:
[tex](80\%)(64.71\%) + (20\%)(x) \ge 70\%[/tex]
↓ rewriting percentages as decimals
[tex](0.8)(0.6471) + 0.2x \ge 0.7[/tex]
↓ subtracting [tex](0.8)(0.6471)[/tex] from both sides
[tex]0.2x \ge 0.7-(0.8)(0.6471)[/tex]
↓ dividing both sides by 0.2
[tex]x \ge \dfrac{0.7-(0.8)(0.6471)}{0.2}[/tex]
↓ evaluating the right side using a calculator
[tex]x \ge 0.9116[/tex]
↓ rewriting as a percentage
[tex]\boxed{x\ge 91.16\%}[/tex]
