1. **Problem 18:** Boyo had a mean score of 80 in two subjects. When the mark of a third subject was added, the mean dropped by 2. Find the third mark. 2. The mean of two subjects is 80, so the total marks for two subjects is: $$\text{Total} = 2 \times 80 = 160$$ 3. When the third subject is added, the mean drops by 2, so the new mean is: $$80 - 2 = 78$$ 4. The total marks for three subjects with the new mean is: $$3 \times 78 = 234$$ 5. To find the third mark, subtract the total of the first two subjects from the total of all three: $$\text{Third mark} = 234 - 160 = 74$$ 6. **Answer for problem 18:** The third mark is **74**. 7. **Problem 19:** The table shows the scores of students in a mental mathematics competition with five questions. Find the fraction of students who scored 80% or more. 8. Scoring 80% or more means scoring at least 4 out of 5 questions correctly. 9. From the table, frequencies for scores 4 and 5 are: - Score 4: 10 students - Score 5: 6 students 10. Total students who scored 80% or more: $$10 + 6 = 16$$ 11. Total number of students is the sum of all frequencies: $$2 + 3 + 4 + 5 + 10 + 6 = 30$$ 12. The fraction of students scoring 80% or more is: $$\frac{16}{30} = \frac{8}{15}$$ 13. **Answer for problem 19:** The fraction is **\frac{8}{15}**.