The reason why fractions with different denominators cannot be added directly is ()

The reason why fractions with different denominators cannot be added or subtracted directly is that the fractional units are different. For example, the decimal unit of 3/4 is 1/4 and the decimal unit of 4/5 is 1/5. (In a fraction, the denominator represents the number of shares divided equally, and one of them is a fractional unit. ) In integer addition and subtraction, the same numbers should be aligned. In decimal addition and subtraction, decimal points should be aligned. All for the same cell alignment. In real life, different units cannot be added or subtracted. For example, between the length unit and the area unit. Another example: how much is three children plus two puppies? If it is equal to 5, it is to treat the puppy as a child; If it is equal to five, it is to treat the child as a puppy and make such a joke. To sum up, addition and subtraction must be carried out in the same company.