1. The problem is to calculate the product $0.1 \times 0.1 \times 0.1 \times 0.1$. 2. The formula for multiplying decimals is to multiply the numbers as if they were whole numbers, then place the decimal point in the product so that the total number of decimal places is the sum of the decimal places in the factors. 3. Each factor $0.1$ has 1 decimal place, and there are 4 factors, so the total decimal places in the product will be $4$. 4. Multiply the numbers ignoring the decimal points: $1 \times 1 \times 1 \times 1 = 1$. 5. Now place the decimal point to have 4 decimal places: $0.0001$. 6. Therefore, the product $0.1 \times 0.1 \times 0.1 \times 0.1 = 0.0001$.