a decagram is 10 grams, so first lets convert the decagrams to grams and then after we'll change to kilograms.
If 1 decagram equals 10 grams, then 2500 decagrams is equal to:
2500*10 = 25000 grams
Now, 1 kilogram equals 1000 grams so 25000 grams equals:
25000/1000 = 25 kg
therefore, 2500 decagrams equals 25 kg