Four teams – Red (R), Blue (B), Green (G), and Yellow (Y) – are competing in the final four rounds of the Inter-School Science Olympiad, labeled Round A, Round B, Round C, and Round D. Each round consists of one match between two teams, and every team plays exactly two matches. No team plays the same opponent more than once.
The final schedule must adhere to the following rules:
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Another way to pin down Green's two rounds is to first work out where Yellow and Blue play, then see what is left over.
Working from Yellow's and Blue's known rounds rather than Red's confirms the same pair: Green's matches sit in Round B and Round C.
So the correct answer is Round B and Round C.
A different way to confirm Round A's match is to try building the rest of the schedule under each option and see which one still allows a complete, consistent four-round timetable.
Only starting Round A with Red vs Blue lets every other round fall into place without breaking any of the rules.
So the correct answer is Red vs Blue.
Another route to the same answer is to first work out who does not play in Round A, since whoever is left over must be the one who does.
With Green and Yellow both absent from Round A, Red is the only team left to face Blue there.
So the correct answer is Red.
Since Round B is already settled as Green against Yellow, working forward from that fact narrows down Round C quickly.
Working forward from Round B's known pairing, Green's second match and Blue's second match both land in Round C, together.
So the correct answer is Green vs Blue.
Another way in is to use Green's schedule as the anchor rather than Yellow's.
Cross-checking against Green's two known rounds still lands on Round A and Round C as the only pair untouched by Yellow.
So the correct answer is Round A and Round C.
A slightly different check is to count every match that actually happens across the tournament and see which team-pairs are simply missing from that list.
Out of the four matches that make up the entire tournament, none of them is Blue against Yellow.
So the correct answer is Blue.
Counting how many rounds each team is supposed to appear in gives another angle on the same conclusion.
Forcing Red down to a single match is exactly what Rule 5's opponent-link condition is meant to prevent, so that is the rule being broken.
So the correct answer is Rule 5 (Opponent Link).
Read the directions carefully and give the answer from the given options.
Who is to the immediate left of K?