Help Please?

In the preparation of a mustard solution, an individual package of mustard was emptied into a beaker and the mass was determined to be 3.809 grams. The mustard was then dissolved in 50.0 ml. of distilled water. The total mass of the solution was found to be 49.401 grams.

Calculate the weight percent of the mustard in the prepared solution.

Is the mass mustard 3.809g or is that the combined weight of the mustard + the beaker. I will assume it's the weight of the mustard alone.

wt% mustard = (wt mustard/wt soln)*100 =
= (3.809g/49.401)*100 = ?
BUT, I'm having trouble explaining how we add mustard of 3.809 g to 50 g H2O and get a total mass of less than 50. It appears to me that we lost about 5 grams somewhere.