Let us write the number of letters for the data we have.
Names of kids: Betty(5), Carol(5), Nick(4), and Joe(3)
Names of colours: green(5), pink(4), red(3), and yellow(6)
Clue #1: No person's name has the same number of letters as his or her favorite color.
From this we understand:
Betty - CANNOT LIKE - GREEN
Joe - CANNOT LIKE - RED
Nick - CANNOT LIKE - PINK
Carol - CANNOT LIKE - GREEN
Clue #2: Carol and the girl who likes pink are in the different grades.
From this we get that Carol and the girl who likes pink are seperate girls. There is only one other girl,Betty.She likes pink
So,Betty likes Pink
Clue #3: Red is the favorite color of one of the boys.
From our table above we know that,
Joe - CANNOT LIKE - RED
Nick - CANNOT LIKE - PINK
Therefore,Nick likes Red.
Now we know 2 of the favourite colours:
Betty - Pink and Nick - Red
Now we have 2 kids(Carol,Joe) and 2 colours(yellow,green) left
From our table above we know that,
Joe - CANNOT LIKE - RED
Carol - CANNOT LIKE - GREEN
Since there are only two colours left,Carol must like yellow.
Then Joe must like green.
To summarize,
Betty - pink
Carol - yellow
Nick - red
Joe - green
Hope this helps,good luck.