Question 946368
Look at the possible outcomes. There are {{{26}}} of them.
RRR RRW RRB RWR RWW RWB RBR RBW RBB
WRR WRW WRB WWR (WWW) WWB WBR WBW WBB
BRR BRW BRB BWR BWW BWB BBR BBW BBB
The WWW outcome is shown in parentheses because it is not really an outcome since there are only 2 white marbles in the urn. 
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So out of those 26 outcomes, there are 19 that have at least 1 blue.
{{{P=19/26}}}