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Google Classroom Task Cards
Join NUMBEROCK under the sea and learn how to multiply by a decimal number using number sense to determine where the decimal point belongs in the product. Then take a peak above the sea where a pirate ship is battling it’s way through a terrifying lightning storm as we review the traditional method of placing the decimal point when multiplying decimals!
Multiplying Decimals Lyrics:
Let’s use our number sense
to multiply nine and one hundredth
by five and one tenth.
We multiply the one to get one, zero, nine.
In the next place value there’s a five.
X holds the place on the second line;
we get a five, a zero, and a forty-five.
Write a line, a plus sign, tally up the score -
to get one-five-nine-five-four.
Let’s think about the reasonableness of our answer
by rounding to a simpler number.
Then we can easily see
where the point needs to be.
Now let’s get intense,
and multiply ninety-two hundredths
by three and two tenths.
Multiply the two, get four and eighteen;
in the next place value is a three.
Write an x to hold the place, and then
we get a six and a twenty-seven.
Add it up and get four, four,
a nine and a two, and there’s one step more.
Here’s another way to place the point worth trying:
look at the numbers you are multiplying,
count the number of decimal places.
In the product move left that many spaces.
If you are interested in getting ideas on how to plan a robust standards-aligned Multiplying Decimals lesson, we recommend checking out Instructure's recommendations for common core standards 5.NBT.1, 5.NBT.4 and 5.NBT.7 . These pages help break down standard language, lay out the grade-appropriate level of rigor for each concept, and offer a variety of suggestions for activities (lesson seeds) that help students achieve their learning targets.