A box contains 10 tablets of medicine A and 15 tablets of medicine B. What is the least number of tablets that should be taken from the box to ensure that at least two tablets of each kind are among the extracted.

A. 12
B. 15
C. 17
D. 19
E. 21

if we extract 12 then it can be all B, but if 17 then 2kinds of each must have to be there like 15B+2A.....
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At least two means 2,3,4,5 etc, so not just even.

12 tablets = 12 B but no A
17 tablets = 15 B and 2 A (even if 15 B extracted)

pick 12 tablets out of the box, chances are that all the 12 tablets are B.
so we have 12 B tablets, not at least two of each kind.

but if we pick 17 tablets out of the box, then even after 15 B we can still have 2 tablets of A.

i mean pick 17 then you have to pick at least 2 from A as well as at least 2 from B.
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Extracting 12 tablets does not guarantee having at least 2 of each type, because all 12 could be medicine B. In such problems you have to consider the worst case scenario.

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Hope it helps.
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