Question

Dr. florenz needs 25 grams of salt for each student to do an experiment. she has 1.2 kilograms of salt on hand. she has a total of 128 students. how much more salt does she need?

Answer 1

First we solve for how much Dr. Florenz needs in total. So:
128 students * 25 grams = 3200 grams
Then we know that she has 1.2 kg or 1200 g (convert from kg into g)
Now, since she needs 3200, we subtract 3200-1200 to find how much she doesn't have, how much she needs. 
The answer is 2000 g or 2 kg