Given data:
The product of a nummber and -7/10 is 1/2.
The given expression can be written as,
[tex]\begin{gathered} (\frac{-7}{10})(a)=\frac{1}{2} \\ a=-\frac{10}{14} \\ =-\frac{5}{7} \end{gathered}[/tex]Thus, the first unknown number is -5/7, so third option is correct.
