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0 / 60 seg.
A scientist puts a bacteria in a petri dish at exactly noon. Every minute the bacteria divides into two and doubles in size. At exactly 1 PM the petri dish is full. At what time was the dish half full?
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Clue
THE DISH WAS HALF FULL AT 12.59 PM. SINCE THE BACTERIA DOUBLES EVERY MINUTE, THEN ONE MINUTE EARLIER, THE DISH MUST HAVE BEEN HALF FULL
THE JAR WILL BE HALF FULL IN 59 MINUTES. A MINUTE LATER, IT WILL DOUBLE AND WILL FILL THE JAR
IT WOULD TAKE 47 DAYS TO COVER HALF OF THE LAKE, AS THEY DOUBLE IN SIZE EVERY DAY
LET'S NAME THE ROPES AS A AND B. LIGHT A FROM BOTH THE ENDS AND B FROM ONE END. WHEN A IS FINISHED BURNING WE KNOW THAT 30 MINUTES HAVE ELAPSED AND B HAS 30 MINUTES REMAINING. NOW, LIGHT THE OTHER NON-BURNING END OF B AND START THE TIMER. WHEN B IS FINISHED BURNING, STOP THE TIMER AS 15 MINUTES HAVE ELAPSED
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