The molality of potassium bromide KBr in an aqueous solution

The molality of potassium bromide, KBr, in an aqueous solution is 2.55 mol/kg. What is the MOLE FRACTION of potassium bromide in the solution?

Can someone please explain how to do this problem?

Solution

2.55 mol/kg  

2.55 moles of KBr present

Moles of water =  1000.0 g / 18.0 g mol¯¹ = 55.6 mol of H₂O

MOLE FRACTION of potassium bromide = 2.55 / (2.55+ 55.6 ) = 0.0438