6.04 Multiply decimals by single digit numbers
Are you ready?
Do you remember how to multiply numbers using a standard algorithm? Let's try this problem to practice.
Find $213\times45$213×45.
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You might notice that sometimes the standard algorithm is called the 'vertical algorithm'. Let's think about why. When we use the standard algorithm, we line our numbers up in 'vertical' place value columns.
Learn
This video looks at using visual models for multiplying decimals.
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Question 1
Use the area model to find $1.27\times8$1.27×8.
Fill in the areas of each rectangle.
$1$1 $0.2$0.2 $0.07$0.07 $8$8 $\editable{}$ $\editable{}$ $\editable{}$ What is the total area of all three rectangles, and therefore the answer to $8\times1.27$8×1.27?
Learn
This video uses the standard algorithm and a couple of methods to check if our answers are reasonable. While this doesn't always tell us our answer is correct, it can definitely help us check our decimal point is in the correct position.
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Question 2
We want to find $1.07\times8$1.07×8.
Will $1.07\times8$1.07×8 be less than or greater than $8$8?
$1.07\times8$1.07×8 is less than $8$8
A$1.07\times8$1.07×8 is greater than $8$8
BFind $1.07\times8$1.07×8, giving your answer as a decimal.
When using a standard algorithm, we multiply the digits together one pair at a time starting from the column that is furthest to the right.