His answer is not correct because when you add fractions, the sum is always greater than 11.
His answer is not correct because the sum cannot be less than either addend.
His answer is correct because 12 + 1 = 1312 + 1 = 13 and 15 + 10 = 2515 + 10 = 25.
His answer is correct because all the fractions are less than 11.