To find out how much Grace saved last December, we need to calculate three-tenths of her paycheck.
Grace's paycheck was $2,500. To find three-tenths of this amount, we perform the following calculation:
\[ \text{Savings} = \frac{3}{10} \times 2500 \]
Calculating this gives:
\[ \text{Savings} = 0.3 \times 2500 = 750 \]
Therefore, Grace saved $750 last December.