[IceRiceIce]

I need help with a question assigned on my chemistry homework. The question reads "Calculate the percentage by mass of 20.0 g NaOH in 140.g water). I know that the formula to find the percent by mass(mass of solute/mass of solution * 100) and the answer I got was 14.3 percent. However, my teacher puts the answers to each equation on the homework and his answer read (12.5 %). Can someone explain to me why his answer varied from mine?

[Meter]

The mass of the solution = mass of solute + mass of solvent

Then you should get 12.5%

You made the mistake of only accounting for the mass of the solvent, which also gives me 14.3%

[IceRiceIce]

Okay, that makes a lot more sense. Thank you!