On a particular sunday an art
museum had 285 visitors and that was 20% of the total number of visitors for that week how many total visitors did the art museum have that week

So, on that 1 day, the art museum had 285 visitors.

So, 285 visitors was 20% of the visitors for that week. (Calculator preferred, you'd do:) 285/0.20.

That would equal:

Your
1425 visitors.

The probability of picking 2 green markers is 2/10