If your average heart rate is 72 beats per minute, how many times will your heart beat per year? And also, if you live until the age of 75, how many times would your heart beat? Let’s begin by writing the rate of 72 beats per minute in fraction form. Where we’d have 72 beats per one minute. And I’ll convert this rate into the number of beats per year using unit fractions and
the conversions given here. So we want the end result
to be in beats per year. We’ll first have to
convert minutes to hours, then hours to days,
and then days to years. So we’ll have to multiply
by three unit fractions, or three fractions equal to
one to perform this conversion. So for the first unit fraction, we want to convert minutes to hours. Because we want minutes to simplify out we have to have minutes
in the numerator here. So that they would simplify
with the minutes here in the denominator. So we’ll convert minutes to hours. And since 60 minutes is equal to one hour, our first unit fraction will
be 60 minutes per one hour. Notice here the units
of minutes simplify out, therefore this product would give us the number of beats per hour. And now we’ll convert hours to days. We want hours to simplify out, and therefore hours must
be in the numerator, and days in the denominator. And 24 hours is equal to one day, so our unit fraction is
24 hours per one day. Notice here hours simplifies out. And for the last unit fraction, we want to convert days to years. We want days to simplify out, so days must be in the numerator and
years in the denominator. Using our conversion, we’d
have 365 days per one year. Once again, notice how
days simplifies out, and therefore this product would
give us the number of beats per one year. Notice how I’m multiplying
the denominators. We just have one. And now we’ll use the calculator to find the product of the numerators. So we’d have 72 times 60 times 24 times 365. So we have 37,843,200 beats per year. Which may also just be written as 37,843,200 beats per year. So some of you may be surprised by this. Notice how your heart
does work pretty hard. And now to answer the
second part of the question, how many times your heart would beat if you lived to be 75 years of age, we have to multiply this rate by 75 years. So we’d have times 75 years. We can put this over one if we want. Notice how the units of
years simplifies out, therefore this product would
give us the number of beats over 75 years. So going back to the calculator, we’ll multiply this result by 75, which gives us 2,838,240,000. Which, once again, is the
number of beats over 75 years if someone’s average heart
rate is 72 beats per minute. So for some of us, we might be surprised how many times our heart
beats over the years. So hopefully this gives us an appreciation for how hard our heart works. I hope you found this helpful.