Time taken by Nina to complete the chapter = was 6 hours.
Amount of chapter completed in 1 hour = 1/6.
[tex]\frac{1}{2}[/tex]Mandy takes the time to complete the chapter = 2 hours.
Amount of chapter completed in 1 hour = 1/2.
Amount of chapters completed by both in 1 hour is calculated as,
[tex]\begin{gathered} For\text{ 1 hour = }\frac{1}{6}+\frac{1}{2} \\ For\text{ 1 hour = }\frac{1}{6}_+\frac{3}{6} \\ For\text{ 1 hour = }\frac{4}{6}\text{ = }\frac{2}{3} \end{gathered}[/tex]Thus the amount of time taken by both of them to complete the chapter is
[tex]\frac{3}{2}\text{ hours or 1.5 hours}[/tex]
