Let’s analyze each scenario step-by-step using fractions.
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Scenario 1:
- Today: Complete \(3 \frac{1}{2} = \frac{7}{2}\) lessons
- Daily: Complete \(4 \frac{1}{2} = \frac{9}{2}\) lessons for 7 days.
Total lessons completed: \[ \frac{7}{2} + 7 \cdot \frac{9}{2} = \frac{7}{2} + \frac{63}{2} = \frac{70}{2} = 35 \] This exceeds 15 lessons, so this scenario does not hold.
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Scenario 2:
- Today: Complete \(3 \frac{1}{2} = \frac{7}{2}\) lessons
- Daily: Complete \(4 \frac{1}{2} = \frac{9}{2}\) lessons for 3 days.
Total lessons completed: \[ \frac{7}{2} + 3 \cdot \frac{9}{2} = \frac{7}{2} + \frac{27}{2} = \frac{34}{2} = 17 \] This exceeds 15 lessons, so this scenario does not hold.
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Scenario 3:
- Today: Complete \(4 \frac{1}{2} = \frac{9}{2}\) lessons
- Daily: Complete \(3 \frac{1}{2} = \frac{7}{2}\) lessons for 4 days.
Total lessons completed: \[ \frac{9}{2} + 4 \cdot \frac{7}{2} = \frac{9}{2} + \frac{28}{2} = \frac{37}{2} = 18.5 \] This exceeds 15 lessons, so this scenario does not hold.
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Scenario 4:
- Today: Complete \(4 \frac{1}{2} = \frac{9}{2}\) lessons
- Daily: Complete \(3 \frac{1}{2} = \frac{7}{2}\) lessons for 3 days.
Total lessons completed: \[ \frac{9}{2} + 3 \cdot \frac{7}{2} = \frac{9}{2} + \frac{21}{2} = \frac{30}{2} = 15 \] This is exactly 15 lessons, so this scenario holds true.
Therefore, the true scenario is Scenario 4: You need to complete 15 math lessons. If you complete \(4 \frac{1}{2}\) math lessons today and \(3 \frac{1}{2}\) lessons per day after that, you can complete the lessons in 3 more days.