Final answer:
To calculate the ventricular rate, the time between R waves is multiplied by the time each small ECG box represents to get the seconds per beat; then 60 seconds is divided by this value to find the beats per minute, which is 75 beats/min.
Step-by-step explanation:
The ventricular rate can be calculated using the number of small boxes on an electrocardiogram (ECG) between R waves, which represent ventricular depolarizations. Each small box on an ECG represents 0.04 seconds. With 20 small boxes between each R wave, you can determine the time between beats: 20 boxes × 0.04 seconds/box = 0.8 seconds between R waves. To convert this time into a rate, you divide 60 seconds by the time it takes for one beat to occur: 60 seconds / 0.8 seconds/beat = 75 beats per minute. Therefore, the ventricular rate is 75 beats/min.