Solution: Let x be the total space of hard drive.
We are given 80% space of hard drive is full and 12000 megabytes are free.
We can write:
![x-80\% * x=12000](https://img.qammunity.org/2019/formulas/mathematics/middle-school/n26dz4plz57lw6qvvr4rauz89y76o0km4s.png)
![x-(80)/(100)x =12000](https://img.qammunity.org/2019/formulas/mathematics/middle-school/te0h1b0xcbv12jnydpwhf41kopoo32gcpb.png)
![(100x-80x)/(100)=12000](https://img.qammunity.org/2019/formulas/mathematics/middle-school/byrh0ojd8qh7iajq5reu4jhrs23bcqa71r.png)
![20x=12000 * 100](https://img.qammunity.org/2019/formulas/mathematics/middle-school/npb207hybvfc312yjewvtlhnitkoio5nrv.png)
![x=(1200000 )/(20)](https://img.qammunity.org/2019/formulas/mathematics/middle-school/et40m7kkgfv9kqo6gr1hor1k1lu4csa972.png)
megabytes
We have to free 5% of space as the difference between 80% and 75% is 5%.
Therefore 5% of 60000 is:
![(5)/(100) *60000=3000](https://img.qammunity.org/2019/formulas/mathematics/middle-school/6h4wykxbw915eu6zx9nkwjdk4u8agzgdde.png)
We know that 1 minute of video uses 60 megabytes of space.
Therefore number of minutes of video that should be deleted to make 75% of space free is:
minutes of video
Hence, 50 minutes of video should be deleted so that the hard drive is 75% full.