A’s father’s wife’s only daughter is B. How is A related to B? (Assuming A is a male member)

Correct — C. Replace each link in the chain with the person it names.

Rule: father's wife = mother, the reading the key takes.

A's father's wife → A's mother
Her only daughter → B, so B is A's sister
A is male → A is B's brother

That is option (c).

Why the others are wrong

• (a)
  Sister — Sister is B's relation to A, the reverse of what is asked. A is male, and B is the only daughter, so A cannot be a sister.
• (b)
  Cousin — Cousin needs different parents. A and B share one mother, A's father's wife, so they are siblings, not cousins.
• (d)
  Uncle — Uncle is a generation above. A and B are children of the same mother, so they stand in the same generation.

Blood-relation chains collapse from the left. A's father's wife is A's mother, so the chain shrinks to A's mother's only daughter, who is A's sister.

The question then flips direction: it asks how A is related to B. A is male, so A is B's brother.

Key facts

• Father's wife is read as mother, and mother's husband as father.
• Two children of the same parents are siblings: brother if male, sister if female.
• 'How is A related to B' asks for A's role, not B's.

Common traps

• Answering Sister, which is B's relation to A, when the question asks for A's relation to B.
• Treating 'father's wife' as someone other than A's mother and reaching for Cousin.

No directly related past PYQ was found.