Question

How many milliliters are equivalent to $2.7$ liters?

Answer 1

Answer:
2700⋅mL
Explanation:
The m prefix in mL means milli, i.e. $\times {10}^{-3}$
And thus $\frac{1.L}{1.mL}=\frac{1.L}{1.\times {10}^{-3}L}=\frac{1}{{10}^{-3}}=\frac{1}{\frac{1}{1000}}=1000,ie.a{10}^3$ factors as required.
Note the arithmetic $\frac{b}{a^{-1}}=\frac{b}{\frac{1}{a}}=a\times b$ this is an important result for such dimensional analysis, as you can see in the given example.