13+313 equals
23+3
13+313
= 13+(13+3)
We know that if we add to any number, three more than itself or if we double the number and add three to it, we get the same number as the result.
i.e., If x is any number, then x+(x+3)=2x+3
So, 13+(13+3)=(2×13)+3
Therefore 13+313 = 23+3