It takes 50 days to fill a laboratory dish with bacteria. If the size of the bacteria doubles each day, how long did it take for the bacteria to fill one half of the dish ?

Options

A. 48 days
B. 24 days
C. 25 days
D. 49 days

Answer

D

Explanation

If the size of the bacteria doubles each day, then the dish must be half full one day before it is full i.e. (50 days-one day) = 49 days. Therefore, the dish will be half full in 49 days.
Important Note: Don.t choose the option (c) blindly i.e. 25 days, as it gives half the time it takes to fill the dish, not the time when the dish is half full. In case, when the dish was one-quarter full, then our answer would have been 48 days i.e (50 days-2 days). [48 days:One-quarter fulli.e. `1/4`th full,49 days:`(1/4 xx 2)` full i.e. `1/2`th full (half full), 50 days: `(1/2 xx 2)` full i.e.completely full].