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11-43.

The big math test is tomorrow! You know that if you have time to study there is a 90% chance of getting a good grade, but if you cannot study there is only a 40% chance of earning a good grade. Your family uses a spinner to see who will have to work at the family business tonight. The spinner has five evenly divided sections and your name is on one section. If you have to work tonight there will be no time to study. What is the probability of getting a good grade? An area model or a tree diagram may be helpful in solving this problem. Homework Help ✎

$\frac{1}{5} \cdot 40\%+ \frac{4}{5} \cdot 90\% = 80\%$