To determine Deepa's age in October 2018, we need to analyze the information provided in each statement and determine which combination of these is sufficient to find the answer.
- From Statement I: "Deepa is 6 years older than her sister Prabha."
- This statement alone gives the age relationship between Deepa and Prabha, but without Prabha's age, we cannot determine Deepa’s age.
- From Statement II: "Prabha is 29 years younger than her mother."
- This statement relates Prabha’s age to her mother’s age. Again, without knowing the mother's age or additional information, we cannot determine Deepa's age.
- From Statement III: "Deepa's mother celebrated her birthday in July 2018."
- This implies that we can mathematically express the ages but still does not give an actual age unless combined with other statements.
Let's now combine the statements:
- Combining Statements I, II, and III:
- Suppose Deepa's mother's age in July 2018 is \( M \). Therefore, Prabha's age is \( M - 29 \).
- From Statement I, Deepa’s age is \( (M - 29 + 6) = M - 23 \).
Since we know the timeline and the exact relationship between each person's age, with their mother's age as a reference from her birthday in July 2018, we can determine Deepa's age using all three statements. Without knowing \( M \), we specifically cannot calculate a numerical age, but these statements are definitely required together to establish a relationship correctly.
Conclusion: Hence, to determine Deepa's age, all three statements I, II, and III are necessary and sufficient. Therefore, the correct answer is: All I, II, and III.