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 ShippedDate IS NOT NULL
      THEN OrderID
  END) AS CountShipped,
  COUNT(OrderID) AS CountAll,
  ROUND(COUNT(CASE
    WHEN ShippedDate IS NOT NULL
      THEN OrderID
  END) / CAST(COUNT(OrderID) AS float), 2) AS ShippedRatio
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.