20 total oranges
5 are bad.
Subtract the bad from the total to find the number of good ones:
20-5 = 15
There are 15 good oranges out of 20 total.
Divide good by total then multiply by 100 to get the percentage:
15/20 = 0.75
0.75 x 100 = 75%
Answer: 75% are good