There are 19C16 = 969 ways for Lester to choose 16 of the 19 objects.
There are 12C11 = 12 ways to choose 11 vases, and 7C5 = 21 ways to choose a non-vase, for a total of (12)(21) = 252 ways to choose exactly 11 vases in 16 objects.
So, the probability of interest is ...
252/969 ≈ 0.2601
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nCk = n!/(k!(n-k)!) ... the number of ways to choose k objects from n
