Question

A human heart pumps about 7 x 10to the -2 power liter of blood per heart beat. The average human heart beats about 72 times per minute. How many liters of blood does a heart pump in 1 year? In 70 years?

Answer 1

`265 × 10^3` litres and `18.6 × 10^6` litres

Explanation:

`(7 × 10^-2 "litre")/cancel"beat" × (72 cancel"beats")/"1 minute" = "5.04 litres/min"`

∴ Heart pumps `"5.04 litres"` of blood in `1` minute.

1. In one year

`"1 year" = 1 cancel"year" × (365 cancel"days")/cancel"year" × (24 cancel"hours")/cancel"day" × (60 cancel"minutes")/(1 cancel"hour") = "525600 minutes"`

`525600 cancel"minutes" × "5.04 litres"/cancel"minute" = "2649024 litres" = color(blue)(265 × 10^3 "litres")`

2. In 70 years

We have already calculated that heat pumps `265 × 10^3 "litres"` in one year.

So,

`70 cancel"years" × (265 × 10^3 "litres")/(1 cancel"year") = 18550 × 10^3 "litres" ≈ color(blue)(18.6 × 10^6 "litres")`