If P is the brother of Q, R is the sister of Q, and S is the father of P, how is R related to S?

Correct — A.
Rule: brothers and sisters share a father.

P is Q's brother and R is Q's sister, so P, Q and R are siblings.
S is P's father, so S is R's father too.

R is a sister, so R is female: R is S's daughter → option (a).

Why the others are wrong

• (b)
  Niece — Niece is the daughter of a brother or sister. That would make S R's uncle, but S is the father of R's brother P, so S is R's father.
• (c)
  Wife — Wife would put R in S's generation. R is a sibling of P, S's child, so R is one generation below S.
• (d)
  Sister — Sister would make R a sibling of S. R's sibling is P, and S is P's father, not his brother.

Place each person on a small family tree and read off the link asked for.

P, Q and R sit on one level as brothers and sisters. S sits one level above P as his father, and siblings share a father, so S is R's parent too. The word sister fixes R as female, which turns child into daughter.

Key facts

• Brothers and sisters share the same parents, so a parent of one is a parent of all.
• 'R is the sister of Q' tells you R is female, whatever Q is.
• A niece is a daughter of one's brother or sister, or of one's brother-in-law or sister-in-law.

Common traps

• Treating Q as male because P is 'the brother of Q': the sentence fixes P's gender, not Q's
• Reading 'S is the father of P' as a link to P alone, and missing that it makes S the father of R as well

No directly related past PYQ was found.