Final answer:
The heart rate is calculated as 100 beats per minute when the distance between two R waves on an ECG is three large boxes. This result is derived by first determining the time per beat in seconds and then converting it to beats per minute.
Step-by-step explanation:
To calculate the heart rate in beats per minute (bpm) when the distance between two R waves is three large boxes on an electrocardiogram (ECG), you can use a standard ECG grid principle. One large box on an ECG grid typically represents 0.20 seconds. Given there are five large boxes per second, this translates to a time per box of 0.20 seconds. The standard paper speed for an ECG is 25 mm/s, and each large box is 5 mm across.
Therefore, the time between two R waves that span three large boxes is:
3 large boxes × 0.20 seconds/box = 0.60 seconds per beat
To convert this to beats per minute, we use the formula:
beats per minute (bpm) = 60 seconds/minute ÷ time per beat in seconds
Plugging in the numbers we find:
60 seconds/minute ÷ 0.60 seconds/beat = 100 bpm
Therefore, the heart rate is 100 bpm, which corresponds to option (c).