3. Used in measuring the width of a wire, one mil is equal to one thousandth of an inch. An inch is about $2.5 \mathrm{~cm}$.
Which of these is approximately equal to one mil?
A $\frac{1}{40} \mathrm{~mm}$
B $\frac{1}{25} \mathrm{~mm}$
C $\frac{1}{4} \mathrm{~mm}$
D $25 \mathrm{~mm}$
E $40 \mathrm{~mm}$
Solution
A

One mil is equal to one thousandth of an inch. An inch is about $2.5 \mathrm{~cm}$, which is the same as $25 \mathrm{~mm}$. Therefore one mil is approximately $\frac{25}{1000} \mathrm{~mm}$, which is the same as $\frac{1}{40} \mathrm{~mm}$.