Multiplying Decimals
How would you model 2 x 0.4?
Now you try: 2.65
x 0.7
Directions for multiplying decimals: 0.7 x 0.3 = 0.21
1. Multiply decimals as you would whole numbers.
2. Then place the decimal point in the product. The number of decimal places in the product is equal to the sum of the number of decimal places in the factors. For example in the problem 0.7 x 0.3 each factor has 1 decimal place, so 1 decimal place + 1 decimal place = 2 decimal places. Place the decimal point in the answer so that you have 2 decimal places. = 7 x 3 = 21 with 2 decimal points = 0.21
Example 1:
6.45 2 decimal places
x 18 0 decimal places
5160
645
116.10 After you place the decimal point, you can drop any remaining zeros at the end of the answer.
Answer: 6.45 x 18 = 116.1
Guided Practice:
1. A family went on a kayak trip down the Androscoggin River. They averaged 3.6 m.p.h. for the 13.5 hours they paddled. How far did they travel? Use rounding to determine if your answer makes sense.
2. A group of 5 friends went out for lunch. Each person had an meal that cost $6.75 and a soda that cost 1.65 each. There is also an 8 % meals tax. How much was the entire bill? It is typical to add 20 % for a tip. How much is the tip? How much is the total cost of everything including the tip?
