In a certain code language, ‘A + B’ means ‘A is the mother of B’; ‘A – B’ means ‘ A is the father of B’; ‘A $ B’ means ‘A is the daughter of B’ and ‘A % B’ means ‘A is the sister of B’. Based on the above, how is P related to S if P + Q − R $ S % T?

Correct — C. Rule: the letter on the left always holds the role — "+" is mother of, "-" is father of, "$" is daughter of, "%" is sister of.

Read P + Q - R $ S % T one link at a time:

P + Q: P is the mother of Q.
Q - R: Q is the father of R, so Q is male.
R $ S: R is the daughter of S.
S % T: S is the sister of T, so S is female.

R has Q for a father and S for a parent, and S is female — so S is R's mother and therefore Q's wife.

P is Q's mother and Q is S's husband, which makes P the husband's mother of S — option (c).

Why the others are wrong

• (a)
  Mother — P is S's husband's mother, not S's own mother. Nobody in the chain is named as a parent of S — the only parent link S has is downward, to R.
• (b)
  Sister’s daughter — Sister's daughter would put P a generation below S. P is the mother of Q, and Q is S's husband, so P stands one generation above.
• (d)
  Sister’s husband — P is female: P + Q reads P is the mother of Q, so P cannot be anyone's husband.

These items give you a private dictionary of symbols and one chain to decode. The dictionary is re-set for every question, so nothing carries over from a code you solved last week.

Two things fix gender. A role word does it directly — mother, father, sister, daughter. A role a person holds towards someone else does it indirectly, which is how Q is fixed as male here, by fathering R.

Decode the chain into short sentences first, then draw two generations with the men and women marked. The relationship asked for usually falls out of the drawing rather than the sentences.

Key facts

• 'A + B' fixes A as female (mother) and 'A - B' fixes A as male (father).
• R is the daughter of both Q and S, and S is female, so S is Q's wife.
• P is the mother of Q, so P is the mother of S's husband.

Common traps

• Reading 'A $ B' as B is the daughter of A — the left letter always holds the role
• Assuming S is male because S sits beside a male in the chain
• Answering 'mother' because P is a mother, without checking whose mother

No directly related past PYQ was found.