How do you calculate mole fraction of solute?

To calculate mole fraction of solute you first calculate the moles of the solute and then you divide that by the total number of moles of solute and solvent.
fraction of is:
moles of solute divided by total moles of solute and
The symbol for the mole fraction is the lower-case Greek letter chi, χ. You will often see it with a subscript: χsolute is an example.
Example 1: 0.100 mole of NaCl is dissolved into 100.0 grams of pure H2O. What is the mole fraction of NaCl?
Solution: We will calculate the number of moles of water ( solvent)
100.0 g / 18.0 g mol-1 = 5.56 mol of H2O

Add that to the 0.100 mol of NaCl = 5.56 + 0.100 = 5.66 mol total

Mole fraction of NaCl = 0.100 mol / 5.66 mol = 0.018

What is the mole fraction of the H2O?
5.56 mol / 5.66 mol = 0.982

Simple, and analytical explanation on this website: https://www.boundless.com/chemistry/textbooks/boundless-chemistry-textbook/solutions-12/concentration-units-93/mole-fraction-and-mole-percent-402-1960/