Find the number of times the human heart beats in the life of 60 years of a man, assuming that the heart beats once in 0.8 s.

The correct option is 2.3668 x 10⁹ s.

To find the total number of times the human heart beats in a lifetime of 60 years, we first calculate the total number of seconds in 60 years and then divide that by the duration of a single heart beat.

First, let us calculate the total number of seconds in 60 years. Assuming a standard year has 365 days:
1 year = 365 days
1 day = 24 hours
1 hour = 60 minutes
1 minute = 60 seconds

Therefore, the total time in seconds for 60 years is:
Total time = 60 years × 365 days/year × 24 hours/day × 60 minutes/hour × 60 seconds/minute

Let us perform the multiplication step-by-step:
60 × 365 = 21,900 days
21,900 × 24 = 525,600 hours
525,600 × 60 = 31,536,000 minutes
31,536,000 × 60 = 1,892,160,000 seconds

Thus, the total time in seconds is:
$$\mathrm{Total\; time}=1.89216��{10}^9\text{s}$$

Given that the heart beats once in every 0.8 s, the total number of heartbeats is the total time divided by the time per beat:
$$\mathrm{Number\; of\; beats}=\frac{1.89216\times {10}^9\text{s}}{0.8\text{s}}$$

Dividing 1.89216 by 0.8:
$$\frac{1.89216}{0.8}=2.3652$$

If we account for the extra leap years in a 60-year lifespan (which adds approximately 15 days, i.e., 60 / 4 = 15 days):
Total days = 60 × 365 + 15 = 21,915 days
Total seconds = 21,915 × 24 × 60 × 60 = 1,893,456,000 seconds
Number of beats = 1,893,456,000 / 0.8 = 2,366,820,000

Expressing this in scientific notation:
$$\mathrm{Number\; of\; beats}\approx 2.3668\times {10}^9$$

Hence, the number of heartbeats (notated with "s" in the option units) is 2.3668 x 10⁹ s.