Many business offices are located in buildings having 2-8 floors. If a building has more than 3 floors, it has a lift. If the above statements are true, which of the following must be true? (2 marks)
2nd floors do not have lifts
7th floors have lifts
Only floors above the 3rd floors have lifts
All floors may be reached by lifts
ANSWER
(b) 7th floors have lifts: any building with a 7th floor has more than 3 floors, so it has a lift.
Official answer: BSource: ISRO's final answer key of 15 May 2026
The statements give one usable rule: if a building has more than 3 floors, it has a lift. The first statement only describes where many offices are (buildings of 2 to 8 floors). It adds no rule about lifts.
Treat each option as a claim about a floor, and ask what that floor tells us about its building. A building that has an -th floor has at least floors.
Option (b): a building with a 7th floor has at least floors, and . By the rule, that building has a lift. This holds for every building that has a 7th floor, so 7th floors always have lifts. (b) must be true.
Option (a): a building with 8 floors has a 2nd floor, and since it has a lift. So a 2nd floor can have a lift, and (a) is not always true.
Option (c): the rule says buildings with more than 3 floors have lifts. It never says buildings with 3 or fewer floors have none. A 3-floor building may or may not have a lift, and floors 1 to 3 of a tall building are in a building with a lift. The word "Only" is not supported, so (c) need not be true.
Option (d): take a building with 2 or 3 floors. The rule does not apply to it, so it may have no lift at all, and then none of its floors can be reached by lift. Nothing in the statements guarantees that every floor can be reached by lift, so (d) need not be true.
The only statement that holds in every case allowed by the given statements is (b): 7th floors have lifts.
KEY IDEA
A floor number tells you the least number of floors its building has. A 7th floor means at least 7 floors, which is more than 3, so the rule applies and that building has a lift. A conditional "if more than 3, then lift" says nothing about buildings with 3 or fewer floors.
WATCH OUT FOR
Picking (d) because "may" sounds weak. It is still a claim about all floors, and a 2- or 3-floor building need not have a lift, so it can fail. A second mistake is reading the rule backwards as in (c), and assuming buildings with 3 or fewer floors have no lift.
From the ISRO EC 2025 paper. Also Q.83 of the ISRO Scientist/Engineer Computer Science 2025 paper. Every question of this paper · The full paper (PDF, ISRO) · All 11 ISRO Reasoning questions, with notes
