UPSC Prelims 2019 · CSAT
Question 29: Data Interpretation
A five-storeyed building with floors from I to V is painted using four different colours and only one colour is used to paint a floor. Consider the following statements :
- 1.The middle three floors are painted in different colours.
- 2.The second (II) and the fourth (IV) floors are painted in different colours.
- 3.The first (I) and the fifth (V) floors are painted red.
To ensure that any two consecutive floors have different colours
AnswerUPSC’s answer is (b).
Four colours are all used on five floors. If floors I and V are both red, the other three colours must fill floors II, III and IV, one each, and none of them is red. Then every pair of neighbours differs, so statement 3 alone is sufficient. Statement 1 alone leaves floor I or V free to match its neighbour, and statement 2 only compares II and IV. Statement 1 already implies statement 2, so adding it gives nothing.
- 1. Not sufficient alone: II, III and IV differ, but I may match II or V may match IV.
- 2. Not sufficient alone: it compares only floors II and IV.
- 3. Sufficient alone: all four colours are used, so II, III and IV take the three non-red colours.
Why each option is right or wrong
- (a) Wrong: statement 2 only compares floors II and IV.
- (b) Right: with I and V red, floors II, III and IV take the three other colours, all different.
- (c) Wrong: statement 2 adds nothing to statement 1, so the pair is still not enough.
- (d) Wrong: statement 3 is already sufficient, so the claim that it is not sufficient fails.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2019, General Studies Paper II (CSAT), Series A. The paper on upsc.gov.in.