To multiply a decimal by a whole number, you can ignore the decimal point at first. Multiply the numbers as if there is no decimal point and then place the decimal point in the product by counting the number of digits after the decimal point in the original decimal.
When multiplying two decimals, you can also ignore the decimal points initially. Multiply the numbers as if there is no decimal point and then place the decimal point in the product by counting the total number of digits after the decimal points in both factors combined.
Estimating before calculating helps us get an idea of what our answer should be. It allows us to check if our calculated answer is reasonable and helps us catch any errors we might have made during calculations.
