Final answer:
The correct compression to ventilation ratio for a single rescuer providing CPR to a 3-year-old is 30 compressions to 2 ventilations, with proper technique to ensure effectiveness.
Step-by-step explanation:
The correct compression to ventilation ratio for a single rescuer performing CPR on a 3-year-old child is 30 compressions to 2 ventilations. This ratio applies to infants and children when a single rescuer is present. It's important to perform these compressions effectively by pushing down on the chest at a depth of about one-third the depth of the chest, at a rate of 100 to 120 compressions per minute. After every 30 compressions, the rescuer should give 2 breaths, ensuring the chest rises with each breath, indicating adequate ventilation.