Final answer:
To store 20GB on 720MB optical discs, one would need 29 discs, as you can't use a fraction of a disc and rounding up to the nearest whole number is necessary.
Step-by-step explanation:
To calculate the number of 720MB optical discs needed to store a 20GB hard disc capacity, we must first make sure both units of storage capacity are in the same units. Since there are 1024 megabytes in a gigabyte, we can convert 20GB into megabytes:
20GB = 20 × 1024MB = 20480MB.
Now, we will divide the total megabytes by the capacity of one optical disc:
20480MB ÷ 720MB/disc = 28.444... discs.
Since you can't use a fraction of a disc to store data, you would need 29 optical discs to store the entire 20GB because you would need to round up to the nearest whole number.