QUESTION

CSAT

Hard

Maths

Prelims 2014

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 Ieast number of tries can the cards be turned upside down such that all the six cards show number '2' on the upper side?

Select an option to attempt

Explanation

Initially, all cards show '1' on the upper side. In each try, exactly four cards are turned upside down. Objective: All cards should show '2' on the upper side.

Step-by-step:

After the first try, 4 cards are flipped, showing '2' on the upper side, and 2 cards still show '1'. After the second try, the same 4 cards are flipped again, but 2 cards that were flipped earlier show '1' again, and the other 2 show '2'. After the third try, all 6 cards will show '2' on the upper side.

Thus, the minimum number of tries required is 3.

Trusted by 2L aspirants