Let's start with the given:
[tex]a<b[/tex] for any a, b such that a and b are real numbers.
Multiplying by [tex]\frac{1}{a}[/tex] on both sides:
[tex](\frac{1}{a})a=1<(\frac{1}{a})b[/tex]
Now multiply by [tex]\frac{1}{b}[/tex] on both sides:
[tex](\frac{1}{b})1=\frac{1}{b}<(\frac{1}{a})b(\frac{1}{b})=\frac{1}{a}[/tex]
Then we have:
[tex]\frac{1}{b}<\frac{1}{a}[/tex]
Then the answer must be c.