Hello!
To calculate percent, it is number of positive cases / number of total cases. So first, we want to find the number of positive cases. You're looking for platinum and silver bands, so just add together the number of platinum and silver bands sold.
Platinum bands: 900
Silver bands: 900
Number of positive cases: 900 + 900 = 1,800
Now, look for the number of total cases. Here, just add together all the band types to get the number of rings bought in total.
Platinum: 900
Silver: 900
Gold: 700
Total number of cases: 900 + 900 + 700 = 2,500
Now, use the equation, and divide the two.
1,800 / 2,500 = .72 = 72%
Therefore, your answer is 72% of the rings sold had a platinum or silver band.
Hope this helps!