Answer: about 20.6 minutes
Explanation:
Given : Lucy can assemble a computer by herself in 35 minutes.
Manny does the same job in 50 minutes.
Let t be the time taken by both of them working together.
Then, we have
![(1)/(t)=(1)/(35)+(1)/(50)\\\\\Rightarrow\ (1)/(t)=(35+50)/(35*50)\\\\\Rightarrow\ (1)/(t)=(85)/(1750)\\\\\Rightarrow\ t=(1750)/(85)=20.5882352941\approx20.6](https://img.qammunity.org/2020/formulas/mathematics/middle-school/v6fmoyeezlg1w44gj6hfvmp28nby75l4kj.png)
Hence, it will take approx 20.6 minutes to assemble a computer working together.