Identify the prices for the base year (2005) and the current year (2010).

Prices in 2005 ($P_0$):
Commodity A: 12
Commodity B: 16
Commodity C: 10

Prices in 2010 ($P_n$):
Commodity A: 20
Commodity B: 25
Commodity C: 12

The formula is:

$$\text{Price Index Number} = \frac{\sum P_n}{\sum P_0} \times 100$$

Substitute the calculated sums into the formula:

$$\text{Price Index Number} = \frac{57}{38} \times 100$$ $$\text{Price Index Number} = 1.5 \times 100$$ $$\text{Price Index Number} = 150$$

The Price Index Number using the simple aggregative method is $\boxed{\text{150}}$.