Question

a student writes 5y*3 to model the relationship the sum of 5y and 3. explain the error

Answer 1

5y*3
This models the relationship as 5y times 3

But the question says to model the relationship as 5y plus 3.

Therefore, the right answer is 5y+3

!!!HOPE THIS HELPS!!!

Answer 2

So,

5y*3 is the open phrase the student uses to model "the sum of 5y and 3".

"The sum of" means addition.  The student put 5y*3, while the sum of 5y and 3 is actually 5y + 3.