Good job! Even though we already computed the final ratio in step 2, we typically also want to round the ratio to a given number of decimal places. To that end, we can use the ROUND(value, decimal_places) function. Take a look:

SELECT
  COUNT(CASE
    WHEN shipped_date IS NOT NULL
      THEN order_id
  END) AS count_shipped,
  COUNT(order_id) AS count_all,
  ROUND(COUNT(CASE
    WHEN shipped_date IS NOT NULL
      THEN order_id
  END) / COUNT(order_id)::decimal, 2) AS shipped_ratio
FROM orders;

We surrounded the last column with the ROUND(..., 2) function invocation. Because the second argument is 2, we'll get the ratio rounded to two decimal places.