Gretchen threw half as many pennies into the fountain as did Rachelle, for a total of 180/2=<<180/2=90>>90 pennies.
Rocky threw one-third as many as Gretchen, for a total of 90/3=<<90/3=30>>30 pennies.
In total, the three threw 180+90+30=<<180+90+30=300>>300 pennies into the fountain.
#### 300