The question reads as such: "What is the mass of a 1.05 µCi carbon-14 source?"

First I convert to decays/s: $R = 1.05 µCi=3.885 \times 10^4 decays/s$.

The half-life for carbon-14 that we've been using is 5730 years or $T_{1/2}=1.808 \times 10^{11} s$, so $\lambda=\frac{ln(2)}{T_{1/2}}=3.834 \times 10^{-12}s^{-1}$

$R=\lambda N$, so $N=\frac{R}{\lambda}=1.0133 \times 10^{16}nuclei$

Now just to convert to grams: $1.0133 \times 10^{16}nuclei \times \frac{1mol}{N_A} \times \frac{12.011g}{1mol}=2.02 \times 10^{-7}g$. Which unfortunately is the wrong answer. Maybe someone sees a conversion error I made somewhere?


Question: Specifying the keyboard layout for Chinese input
Answer: You set the Latin keyboard layout for Japanese input in the Kotoeri Preferences.  For Chinese, the IM normally uses the last Latin keyboard layout that you have used.

Settings you make in the system preferences/language &amp; text/language or formats tab are irrelevant for the keyboard layout.  Only the input sources tab affects that (and Kotoeri preferences when that is chosen as an input source).