Here's why:
* Decagram: A decagram is a unit of mass equal to 10 grams.
* Hundred Decagrams: Therefore, a hundred decagrams is 100 x 10 grams = 1000 grams.
* Kilogram: A kilogram is a unit of mass equal to 1000 grams.
So, "one kilogram" is the synonym for "hundred decagrams".