It happened because the data types for columns game1, game2,...game5 were taken as VARCHAR

The below code will avoid the issue

; WITH cte_Students AS

(

SELECT*,

CASE WHEN SUBSTRING(rate, 1, 1) = '*' THEN 10 /*The previous version had apostrophes here which made the data type of the column as VARCHAR*/ ELSE SUBSTRING(rate, 1, 1) END AS game1,

CASE WHEN SUBSTRING(rate, 2, 1) = '*' THEN 10 ELSE SUBSTRING(rate, 2, 1) END AS game2,

CASE WHEN SUBSTRING(rate, 3, 1) = '*' THEN 10 ELSE SUBSTRING(rate, 3, 1) END AS game3,

CASE WHEN SUBSTRING(rate, 4, 1) = '*' THEN 10 ELSE SUBSTRING(rate, 4, 1) END AS game4,

CASE WHEN SUBSTRING(rate, 5, 1) = '*' THEN 10 ELSE SUBSTRING(rate, 5, 1) END AS game5

FROMstudents

)

SELECT*, ( game1 + game2 + game3 + game4 + game5 ) / 5.0 /*Made 5 as 5.0 to avoid integer conversion*/ AS [percent]

FROMcte_Students