In this question, three statements are given, followed by three conclusions numbered I, II and III. Assuming the statements to be true, even if they seem to be at variance with commonly known facts, decide which of the conclusions logically follow(s) from the statements. Statements: All computers are printers. Some printers are laptops. All laptops are mobiles. Conclusions: I.Some printers are computers. II.Some laptops are printers. III. Some mobiles are laptops.

Correct — D.

Rule: each conclusion here is one statement read backwards — no chain across two statements is needed.

Conclusion I. All computers are printers puts every computer inside printers. Something inside printers is therefore a computer, so Some printers are computers follows.

Conclusion II. Some printers are laptops describes an overlap. The same overlap seen from the other side reads Some laptops are printers, so it follows.

Conclusion III. All laptops are mobiles puts every laptop inside mobiles, so Some mobiles are laptops follows.

All three hold, which is option (d).

Why the others are wrong

• (a)
  Only conclusions II and III follow. — Drops conclusion I. All computers are printers still guarantees an overlap between the two groups, and an All statement always yields the matching Some when reversed.
• (b)
  Only conclusion III follows. — Keeps only the third statement's reversal. It treats the first and second statements as unusable, but each of them turns directly into its own conclusion without help from the others.
• (c)
  Only conclusions I and III follow. — Drops conclusion II. Some printers are laptops and Some laptops are printers state exactly the same overlap — a Some statement reads the same in either direction.

Most three-statement syllogisms are solved by combining premises, but a conclusion can also follow from a single statement turned round. That move is called conversion, and it is the whole of this question.

All A are B converts only into Some B are A. Some A are B and No A are B convert fully, giving Some B are A and No B are A.

So before drawing any diagram, test each conclusion against the single statement that shares its two terms. If it is a legal conversion, it follows, and nothing else has to be checked.

Key facts

• All A are B yields Some B are A, and never All B are A.
• Some A are B and Some B are A are the same statement.
• No A are B and No B are A are the same statement.
• Every conclusion in this item shares its two terms with exactly one of the three statements.

Common traps

• Hunting for a chain across two statements when one statement already gives the conclusion.
• Treating All A are B as reversible into All B are A.
• Rejecting a Some conclusion because the statement it came from said All.

No directly related past PYQ was found.