Question 1
Six identical cards are placed on a table. Each card has number '1' marked on one side and number '2' marked on its other side. All the six cards are placed in such a manner that the number '1' is on the upper side. In one try, exactly four (neither more nor less) cards are turned upside down. In how many least number of tries can the cards be turned upside down such that all the six cards show number '2' on the upper side?
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Correct AnswerA
Explanation
Each move flips exactly four cards. Three moves suffice: choose overlaps so that all six cards have been flipped an odd number of times.