Answer: 2:3
Explanation:
Given : Duration of first aid training received by lifeguard=15 hours.
Duration of cardiopulmonary resuscitation (CPR) training received by lifeguard=10 hours
Now, The ratio of hours of CPR training to hours of first aid training
=10:15

As 10 and 15 , both are the multiples of 5, thus divide both (numerator and denominator ) by 5, we get

∴The ratio of hours of CPR training to hours of first aid training=2:3