There are 2 tablets of type "A" and 2 tablets of type "B".
You are supposed to take one tablet of "A" and one tablet of "B" daily.  (i.e. the given 4 tablets last for 2 days.)

Upon taking medicines on the first day, unfortunately 2 tablets of "B" get mixed up with one tablet of "A".

Both tablets of types of "A" and "B" look similar.

Question :
How will you take medicine ensuring one tablet of each type "A" and "B"?
Remember you should not consume either 2 tablets of "A" or 2 tablets of "B" for that would spell fatal to you.

See answer