Question

50 ml of a solution of 50% dextrose is added to a liter of 0.45% NaCl with 2.5% dextrose to yield a solution with a final dextrose concentration of what percent

Answer 1

The NaCl does not count in this case.
(50ml * 50% + 1000 ml * 2.5%)/(50 ml+1000ml)
=4.76%

Answer 2

4.8%

Answer 3

Where did this 1000mL come from?

Answer 4

1 L is equal to 1000 mL. The liter is converted into mL to match the unit of "Fifty mL"