To find the number of green apples in the basket, we can subtract the number of red apples from the total number of apples.
Total apples = 18
Red apples = 5
Green apples = Total apples - Red apples = 18 - 5 = 13
Now, to find the ratio of the number of red apples to the number of green apples, we express it as follows:
Ratio of red apples to green apples = Red apples : Green apples = 5 : 13
Therefore, the ratio of the number of red apples to the number of green apples is 5:13.