CH2O is a general formula for any carbohydrate. One can recognize a carbohydrate because the ratio of hydrogen atoms to oxygen atoms is 2:1 as in the formula CH2O. However, when one specifically looks at different carbohydrates like glucose(monosaccharide), maltose(disaccharide) or starch(polysaccharide), the number of atoms will differ changing the formula. However, there will always be twice as many hydrogen atoms as oxygen. If you look at the formula for glucose, it is C6H12O6. The least common denominator is 6. If you divide the 12 Hydrogen atoms in the equation by 6, the result is 2. If you divide the 6 oxygen atoms by 6, the result is 1. The 2:1 oxygen ratio is there, in the formula! Therefore, it fits with the general rule for recognizing a formula that represents carbohydrates. Every sugar will have its own molecular formula.