A man smokes a cigarette of length 6 cm (Butt size not included). It takes him 2 seconds to take one puff and his inhaling capacity burns 3 mm of cigarette in one puff. After taking a puff he rests for some time and takes another puff. Even if he does not smoke the air has the capacity to burn 1 mm in 1 second. He completes his cigarette in 30 seconds. How many puffs he takes in completing one cigarette. (Assume that he completes the cigarette with a complete puff)
12
15
10
None of the above.
Cannot be determined.
Answer :10
Solution (Fast Approach)
The man takes 2 sec for 1 puff. He burns 3 mm by inhaling.
Trick: When he is taking puff, air is also doing its work. Hence in 2 seconds air burns 2 mm cigarette.
Thus in 1 puff a total of 3 + 2 = 5 mm is burnt
Let us assume that he takes x puffs and for y seconds he is not smoking
Cigarette length is 60 mm. Hence 5x + y = 60 (Air burns 1 mm in 1 sec, hence y mm in y sec) ... equation 1
Total time taken in smoking = 30 sec. Hence 2x + y = 30 ... equation 2
Solving equation 1 and 2 we get, x = 10
Hence he takes 10 puffs to complete the cigarette
Note: The assumption is given to make sure that he does not complete the cigarette in partial puff.
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