posted by Dexter .
What is the gram formula mass of NaC2H3O2 multiplied by 10H2O
You are greatly in error in your terms.
NaC2H3O2.10H2O the 10H20 is not multiplied, it is added to get the total formula mass. Water of hydration is often written in formulas with a separation sign from the main formula as an "addon", indicated the water is physically attached in the crystal. Physically, as opposed to chemically.