A 6 cm long cigarette burns up in 15 minutes if no puff is taken.For every puff, it burns three times as fast during the duration of the puff.If the cigarette burns itself in 13 minutes, then how many puffs has the smoker taken if the average puff lasted 3 seconds?

Explanation:-

Let the number of puffs abe,
3x * (3 * ¹/₁₅₀) + ( 13 * 60 - 3x) * ¹/₁₅₀ = 6
On solving, We get, x = 20 puffs.