Decimal by Decimal Multiplication Review

Multiply Decimals Test Review

by Mr. Lasaitis

Fill in the Blank

Use the number line to answer the question. James bought 5 airheads for $0.20 each. If James used the number line, he would start on 0.2 for the cost of one piece of gum. He moves ____ hash marks more to show he bought a total of 5 airheads.

​Explanation

​James starts at 0.20 which is the first hash mark. He needs to move 4 more hash marks to show that he bought 5 airheads. The total cost should end up at $1.

Multiple Choice

What is the product of 0.26 x 40? Hint* you cannot rely on using just decimal place value to answer. You will need to solve it first.

• 10.04

• 10.4

• 1.04

• 104

​Explanation

​Because 10.4 = 10.40, my product does have two decimal place values but we do not always need to write the 0 in the hundredths place if there are no numbers to the right of it.

Multiple Choice

What decimal multiplication equation is being shown? Hint* this is a hundredths grid

• 50 x 20 = 100

• 0.50 x 0.20 = 0.70

• 0.50 x 0.20 = 0.10

• 5 x 2 = 10

​Explanation

​Each color represents a number in the model. In this example the grey shows 5 full columns, which is equal to 0.50 (5 tenths or 50 hundredths). The pink is equal to 0.20 (2 tenths or 20 hundredths). Where they overlap, shows the product of 0.10 (1 tenth or 10 hundredths).

Multiple Choice

Mildred solve the problem 1.15 x 1.6. Which shows the correct work to find the product? Hint* think about how the decimal moves with powers of ten.

• (115 x 1/10) x (16 X 1/10)

  (115 x 16) x (1/10 x 1x10)

• (115 x 1/100) x (16 x 1/10) 

  (115 x 16) x (1/100 x 1/10)

• (115 x 1/10) x (16 x 1/100)

  (115 x 16) x (1/10 x 1/100)

• (115 x 1/100) x (16 x 1/100) 

  (115 x 16) x (1/100 x 1/100)

​

​1.15 x 1.6 =

(115 x 1/100) x (16 1/10)

​(115 x 16) x (1/100 x 1/10)

​

​This opportunity is all about place value. The fractions tell us to move the decimal. The decimal place value in the product must equal the sum of the decimal place value in both factors.