5I.13 (b) - 7th edition - sig figs

[Andie Jian 1D]

In this question, we are supposed to calculate the equilibrium composition. I got the quadratic equation 0= 4x²+1.2*10^-4x-1.2*10^-7, which led to x being 1.6*10^-4. [F2]=1.0*10^-3-x, so I got the answer 8.4*10^-4. However, the answer key gives the answer with just two sig figs, making it 8*10^-4. Did I miscalculate the number of sigfigs in this problem?

[Ana Pedreros]

8*10^-4 has one sig fig because you only count the sig figs in the number being multiplied. I believe Lavelle has stated that 2 decimal places for the answer is acceptable for these problems.