I found an answer from worldbuilding.stackexchange.com

I'm stranded on an alien planet. How do I measure an earth year ...

Use a stick to create a sundial. Now start counting your heartbeats. Very roughly you can expect ~5,000 per hour (80 BPM). Make marks where the shadows lie ...

For more information, see I'm stranded on an alien planet. How do I measure an earth year ...

I found an answer from infolab.stanford.edu

4 Combinatorics and Probability

combinatorics. The concepts that surround attempts to measure the likelihood of ... problem is counting the number of anagrams of a word that may have some ... Probabilistic reasoning and ways that we can estimate probabilities of com- ... thus the number of possible outcomes of the sort will be equal to Π(n), the number.

For more information, see 4 Combinatorics and Probability

I found an answer from phys.libretexts.org

1.3: Accuracy, Precision, and Significant Figures - Physics LibreTexts

Oct 25, 2020 ... You measure the length of the paper three times and obtain the ... Usually an object with unknown mass is placed in one pan and ... This indicates a low precision, high accuracy measuring system. ... is an uncertainty in anything calculated from measured quantities. ... 1.2: Physical Quantities and Units.

For more information, see 1.3: Accuracy, Precision, and Significant Figures - Physics LibreTexts

Like the precise measurements in science are required, reasonable approximations of physical quantities using rudimentary ideas and general observations are equally valuable.

a) \text{ Density } = \frac{\text{ mass }}{\text{ volume }}

Total mass of rain fall can be determined with knowledge of rainfall volume and water density.

Density of water = 10^{3} kgm^{-3}   

During the monsoon, the height of the water is measured h = 215 cm = 2.15 m

Area of the earth A = 3.3 * 10^{12} m^2   

Volume of the rain fall = Ah = 3.3 * 10^{12} m^2 * 2.15 m   

= 7.1 * 10^{12} m^3

Total mass of rain fall = \text{ Density * volume } = 10^{3} kgm^{-3} * 7.1 * 10^{12} m^3

= 7.1 * 10^{15} kg

b)We can estimate the mass of the elephant mass using the Archimedes principle

As per the Archimedes principle, the upward buoyant force exerted on a body immersed in a fluid, whether partially or completely submerged, is equivalent to the weight of the fluid that the body displaces.

Displaced water mass =(displaced water volume)x (density of water)

When elephant is immersed in water, measure the volume of water displaced = V

Displaced water mass = V *10^{3} kgm^{-3}   

Mass of water = Mass of object

hence, estimated mass of the elephant = V *10^{3} kgm^{-3}   

c)  To measure the wind speed a rotating device( anemometer) can be used. When the wind blows, wind speed is given by the number of rotations per second.

d) Area of the head surface = A

Measure the radius of the hair using the screw gauge =  r

Area of the hair a = \pi r^2   

The number of hair strands = \frac{\text{ Area of the head surface }}{\text{ Area of the hair }}   

= \frac{A}{a} = \frac{A}{\pi r^2}

e) Calculating the number of molecules of air in the classroom

Volume of the class room V_c = lbh where, l -length, b-breadth and h - height

Volume of the air molecule(sphere in shape) V_a = \frac{4}{3} \pi r^3   where, r- radius of the air molecule

Number of molecules of air = \frac{V_a}{V_c}

= \frac{ \frac{4}{3} \pi r^3 }{lbh}

= \frac{4 \pi r^3 }{3 * lbh}

Hence, number of molecules of air in the classroom = \frac{4 \pi r^3 }{3 * lbh}