You have 18 rainy out of 90 total. You need to simplify each term.
18 = 1, 2, 3, 6, 9, 18
90 = 1, 2, 3, 5, 6, 9, 10, 15, 18, 30, 45, 90
Now find the largest number that is common. That would be 18. Divide both numbers by 18
18/18 = 1
90/18 = 5
So the simplified ration is 1/5
