On the first day, Cleo and Ignacio took 3/5 * 30 marbles = <<3/5*30=18>>18 marbles from the jar
When they shared the marbles, each got 18 marbles / 2 people = <<18/2=9>>9 marbles/person
The total number of marbles remaining in the jar is 30 marbles - 18 marbles = <<30-18=12>>12 marbles
On the third day, Cleo took 1/2 * 12 marbles = <<1/2*12=6>>6 marbles from the jar.
The total number of marbles she has on the third day is 6 marbles + 9 marbles = <<6+9=15>>15 marbles.
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