Solution:
Solution
Given: an urn containing 20 tickets, and 2 tickets are drawn without replacement
To find: the probability that both the tickets show even number
Sol: According to the question
$$n(S)=20$$
There are 10 even numbers between 1 to 20.
Therefore, the probability that both the tickets show even number is
$$=\dfrac {10}{20}\times \dfrac {9}{19}=\dfrac 9{38}$$