Lesson 9.8:
Multiplication of Decimals
Mental Math
estimate the product and write the
number model you used to solve it
Example:
9 * 18
You write:
or
11 * 42
63 * 63
9 * 20 = 180
10 * 18 = 180
22 * 76
98 * 59
28 * 49
72 * 414
Math Message
Solve the problem at the top of MJ
page 268
Estimating Products of Decimals
We will learn to find the product
of decimals
On your slate, estimate each product.
Show your work.
11 * 2.8
110 * 2.8 11 * 0.28
11 * 2.8
110 * 2.8
11 * 0.28
Which problem is most likely to have the
product 30.8? How do you know?
110 * 2.8 = 308
Where would you place the decimal point?
How do you know?
11 * 0.28 =
308
Where would you place the decimal point?
How do you know?
Estimate the cost of 5 calculators
Multiply 5 * 929
Let’s use our estimate to place the
decimal.
What are the steps to estimating
the product of decimals?
Partnership Work MJ p 268
Math Journal page 269
What did we learn…