Problem 12 · 2019 Math Kangaroo
Medium
Logic & Word Problems
work-backward
There are white, grey and black squares. Three children use these to make this pattern. First Anni replaces all black squares with white squares. Then Bob replaces all grey squares with black squares. Finally Chris replaces all white squares with grey squares. Which picture have the three children now created?
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Answer: A
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Hint 1 of 2
Do the three colour changes one at a time, in the order Anni, then Bob, then Chris.
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Hint 2 of 2
Follow just one square of each starting colour all the way through to see what it turns into.
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Approach: follow each starting colour through the three changes in order
- A black square turns white (Anni), then that white turns grey (Chris), so black ends grey.
- A grey square turns black (Bob) and stays black, so grey ends black.
- A white square is only changed by Chris, turning grey, so white ends grey.
- Recolouring every square this way gives the picture in option A.
Mark:
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