An inhaler contains 200 puffs. A patient uses 6 puffs/day for 20 days, then reduces to 4 puffs/day. How long will the inhaler last in total?

Correct option is B

First 20 days = 6 × 20 = 120 puffs. Remaining = 200 – 120 = 80 puffs left. At 4 puffs/day, this lasts 20 more days, giving 40 days total.
Explanation of options: (a) ✘ 35 days underestimates, as full 80 puffs remaining would last longer. This ignores the second phase fully. (b) ✔ Correct; total of 40 days = 20 days at higher dose + 20 days at lower dose. This matches calculations. (c) ✘ 45 days would require 220 puffs, which exceeds the inhaler’s total of 200. (d) ✘ 50 days would need 240 puffs, impossible with only 200 available.