How many times does a heart beat in a lifetime?

Question

Take a resting heart rate of about 70 beats per minute and a lifespan of about 80 years. Solve in your head. Roughly how many times does a human heart beat in a lifetime? Aim: under 30 seconds.

Accepted Answer

Chain the factors, building up one unit at a time. - Per hour: 70 	imes 60 = 4{,}200 beats. - Per day: 4{,}200 	imes 24 = 100{,}800, call it \approx 1.0 	imes 10^5. - Per year: 1.0 	imes 10^5 	imes 365 \approx 3.7 	imes 10^7 beats. - Per lifetime: 3.7 	imes 10^7 	imes 80 \approx 2.9 	imes 10^9. \approx 3 	imes 10^9 	ext{ beats, about 3 billion.} Takeaway. Fermi chains work best when you round to one clean significant figure at each hop (24 	imes 4200 \approx 10^5/day) and carry powers of ten separately. The 3-billion-beats figure is a classic order-of-magnitude sanity number.

How many times does a heart beat in a lifetime?

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