Question

Which of the following is the best estimate for the mass of all the people living on Earth? (a) 2 x 10⁸ kg (b) 1 x 10⁹ kg (c) 2 x 10¹⁰ kg (d) 3 x 10¹¹ kg (e) 4 x 10¹² kg

Answer 1

Step-by-step explanation:

a little check on the internet tells us that there are currently about 8.1 billion people alive in Earth.

8.1 billion = 8,100,000,000 = 8.1 × 10⁹

so, if everybody weighed only 1 kg (which we don't), then (a) and (b) are already too small and out.

if everybody weighed 2 kg (which we don't), then that would be

2×8.1 × 10⁹ = 16.2 × 10⁹ = 1.62 × 10¹⁰

that is about (c). so, (c) is out.

if everybody weighed 40 kg (which I think is too low), then that would be

20 × 1.62 × 10¹⁰ = 32.4 × 10¹⁰ = 3.24 × 10¹¹

this is about (d) and should be out for being too little.

but (e) would be more than 10 times (d), which would mean everybody weighed more than 10×40 = 400 kg. that is definitely not the case. (despite all the obesity in the world, but 400+ kg people are a tiny, tiny extreme fraction of the world population, so that cannot be our mean value).

so, the most realistic estimate is then

(d) 3 × 10¹¹ kg