Question

A human hair is approximately $0.005\mathrm{mm}$ in diameter. How many hair are required to reach the thickness of $1\mathrm{m}$?

Answer 1

We have,

Thickness (diameter) of human hair$=0.005\mathrm{mm}$

Required thickness$=1\mathrm{m}$

We know that,

$1\mathrm{m}=1000\mathrm{mm}$

Thus, number of hair required to reach the thickness of $1\mathrm{m}(1000\mathrm{mm})=1000÷0.005$

$$\begin{gathered} =\frac{1000}{0.005} \\ =\frac{1000\times 1000}{0.005\times 1000}[\mathrm{Multiplying}\mathrm{numerator}\mathrm{and}\mathrm{denominator}\mathrm{by}1000] \\ =\frac{1000000}{5} \\ =200000 \end{gathered}$$

Hence, $200000$ hair of $0.005\mathrm{mm}$ are required to reach the thickness of $1\mathrm{m}$.