Answer:
3. 72 questions
4. 180 students
5. 120 students
6. 9 puzzles
Explanation:
Question 3
![\begin{aligned}\implies \rm 80\% \;of \; 90 \; questions & =80\% * 90\\&= (80)/(100) * 90\\& = (7200)/(100)\\& = 72\end{aligned}](https://img.qammunity.org/2023/formulas/mathematics/college/nlolt8u39rtdm52gnzip4apc0xuwlgdgut.png)
Therefore, a student must answer 72 questions correctly to pass the test.
Question 4
![\begin{aligned}\implies \rm 40\%\; of\; 450\; students & = 40\% * 450\\& = (40)/(100) * 450\\& = (18000)/(100)\\& = 180\end{aligned}](https://img.qammunity.org/2023/formulas/mathematics/college/r7btkvxt3udfmc9p680u6jp6pqqo8oip9h.png)
Therefore, at least 180 students must plan to attend in order for the school to have the festival.
Question 5
![\begin{aligned}\implies \rm 40\% \; of \; 300 \; students & = 40\% * 300\\& = (40)/(100) * 300\\& = (12000)/(100)\\& = 120\end{aligned}](https://img.qammunity.org/2023/formulas/mathematics/college/q0kwm734xggsoppd9ag5x0jh31uhutlliu.png)
Therefore, 120 students chose recycling.
Question 6
If 55% of 20 puzzles are completed, then 45% of 20 puzzles are left to complete, since 100% - 55% = 45%.
![\begin{aligned}\implies \rm 55\% \; of \; 20 \; puzzles & = 45\% * 20\\& = (45)/(100) * 20\\& = (900)/(100)\\& = 9\end{aligned}](https://img.qammunity.org/2023/formulas/mathematics/college/51q5zb2558uvcbf4wuqjtz3eluxt44js3d.png)
Therefore, Magdalena has 9 puzzles left to complete.