Reasoning : Logical Reasoning & Analytical Ability

Q 104 / 325

UPSC CSE Prelims 2021

Half of the villagers of a certain village have their own houses. One-fifth of the villagers cultivate paddy. One-third of the villagers are literate. Four-fifth of the villagers are under 25 years of age. Which one of the following statements is certainly correct?

EXPLANATION

Correct Option (2)

Let's define the given proportions of villagers:

  • Villagers with own houses: 1/2 = 50%
  • Villagers cultivating paddy: 1/5 = 20%
  • Literate villagers: 1/3 ≈ 33.33%
  • Villagers under 25 years of age: 4/5 = 80%

To determine the minimum percentage of overlap between two groups, A and B, we can use the principle of inclusion-exclusion. The minimum overlap is given by P(A) + P(B) - 100%. If this sum is less than 0%, the minimum overlap is 0%.

For Option 2, we consider villagers under 25 years of age (80%) and literate villagers (33.33%).

Minimum overlap = 80% + 33.33% - 100% = 113.33% - 100% = 13.33%.

Since the minimum overlap is 13.33%, it is certain that at least 13.33% of the villagers possess both characteristics (being under 25 and literate). Therefore, the statement "Some villagers under 25 years of age are literate" is certainly correct.

Incorrect Options:

  • Option 1: All the villagers who have their own houses are literate.
    • Villagers with own houses constitute 50% of the total, while literate villagers constitute approximately 33.33%.
    • For all villagers with houses (50%) to be literate, the literate population would need to be at least 50%. However, it is only 33.33%. This makes the statement impossible and thus certainly incorrect. The maximum possible overlap between these two groups is 33.33%.
  • Option 3: Only half of the villagers who cultivate paddy are literate.
    • Villagers cultivating paddy are 20%, and literate villagers are 33.33%.
    • "Only half of the villagers who cultivate paddy" implies that exactly 10% (half of 20%) of the total villagers are both paddy cultivators and literate.
    • The actual overlap between these two groups can range from a minimum of 0% (since 20% + 33.33% - 100% is negative) to a maximum of 20% (the smaller of the two percentages).
    • Since the overlap is not fixed at 10%, this statement is not certainly correct.
  • Option 4: No villager under 25 years of age has his own house.
    • Villagers under 25 years of age are 80%, and villagers with own houses are 50%.
    • To find the minimum overlap: 80% + 50% - 100% = 130% - 100% = 30%.
    • This indicates that at least 30% of the villagers are both under 25 and have their own house. Therefore, the statement "No villager under 25 years of age has his own house" is certainly incorrect.