Discover what the clues do not say
Can a code tell you everything?
For these three checks only, + means “is father of” and − means “is mother of”. Look at X − Y + Z. Predict each plain-language fact before looking at an answer. The final check deliberately asks for more information than the code gives.
Here + means “is father of” and − means “is mother of”. In X − Y + Z, what does X − Y state?
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Correct answer: A
Read each pair using the local definition: left person X is mother of right person Y. These are not arithmetic operations.
Option A: Correct: the minus symbol says the left person X is the mother of the right person Y.
Option B: This reverses the left and right people. The key starts with X, not Y.
Option C: Neither symbol in the key means marriage.
Option D: Father is the plus symbol here; the question asks about the minus symbol.
Hint: Decode one pair at a time.
With those definitions, what is X to Z in X − Y + Z?
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Correct answer: B
X is Y’s mother; Y is Z’s father. From Z, go to father Y and then his mother X: paternal grandmother.
Option A: The middle person Y is Z’s father, not Z’s mother, so this is not the maternal branch.
Option B: Correct: X is the mother of Z’s father Y, so X is Z’s paternal grandmother.
Option C: This drops the intermediate person Y and one generation.
Option D: Both links are parent links; they do not put X and Z in a sibling relation.
Hint: Write two plain sentences before naming the relation.
In X − Y + Z, can we conclude that Z is X’s grandson?
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Correct answer: C
Z is X’s son’s child. The code fixes X and Y, not Z’s gender. Grandchild is established; grandson is not.
Option A: Grandchild is known, but grandson additionally requires Z to be male. That fact is missing.
Option B: The clues do not force Z to be female either. Unknown does not mean the opposite gender.
Option C: Correct: Z is X’s son’s child, but no clue says whether Z is a son or daughter.
Option D: X is definitely a grandparent: X is parent of Y, and Y is parent of Z.
Hint: A relation word can require one more fact than a generic term.
Find the boundary of the evidence
Try two possibilities: Z is a boy; Z is a girl. Do both fit X − Y + Z? If yes, the code cannot force “grandson”. This is a small counterexample test, not a speed trick. Read the summary, then apply it to new symbols in the separate practice.
A code is a small dictionary
A symbol has only the meaning supplied in that question. There is no universal blood-relations meaning of +, −, @ or #. These expressions are not arithmetic: do not use BODMAS.
For our example only: A + B means A is B’s father. A − B means A is B’s mother. Read X − Y + Z as two facts: X is Y’s mother; Y is Z’s father. Both facts must stay true together.
Write the facts before answering. Parent map: X → Y → Z. From Z, go to father Y, then his mother X. X is Z’s paternal grandmother. But Z’s gender is unknown, so “Z is X’s grandson” is not proved.
“Not determined” is a conclusion about the information, not a guess. Name the missing fact. If two different answers fit all the given clues, one exact answer has not been established.
Now take the separate practice
Open this lesson’s Practice test: five new checks, about eight minutes, with explanations after answering. This is a low-stakes learning check, not an official SSC paper. Try without the notes, then return to the exact step that caused an error. The optional time estimate is not an exam speed target.
Comparison note: these prototype modules use parallel versions of the same skills. Repeated exposure can improve your score, so this is a format comparison, not a controlled experiment proving which method is best.
Design inspiration: Brilliant’s learning approach. The explanations and questions here are original; this is not an official Brilliant course.
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