Topic 4: Multiplying Decimals

Topic 4: Multiplying Decimals

by Brad Drey

Topic 4- Multiplying Decimals

Multiplying Decimals by Powers of 10

• What are the powers of 10? Which way do we move the decimal when we multiply by a power of 10?

• Solve: 3.45 x 10,000 = ?

• Solve: 0.34 x 10³ = ?

Estimating Products of a Decimal

• 2 Strategies: Rounding or compatible numbers

• Estimate the product: 34 x 1.93 = ?

• Estimate the product: 126 x 4.2 = ?

Poll

Ms.Moore went to the store and bought 9 packs of water bottles for $3.37 each. About how much did she spend?

What should we round $3.37 to.... which is it closest too?

• $3.00

• $4.00

Poll

Ms.Moore went to the store and bought 9 packs of water bottles for $3.37 each. About how much did she spend?

If we round to $3 what should our answer be closer to?

• 27

• 36

Poll

Ms.Moore went to the store and bought 9 packs of water bottles for $3.37 each. About how much did she spend?

Is this an over or under estimate?

• over estimate

• under estimate

Multiple Choice

You multiply decimals the same way you multiply multi-digit whole numbers.

• True

• False

Multiple Choice

4.183x100=

• 41.83

• 418.3

• 4183

Multiple Choice

Sandra can run 6.2 miles in one hour. How many miles could she run in 10 hours?

• 16.2 miles

• 62 miles

• 620 miles

Multiple Choice

4.4x3=

• 7.4

• 7.7

• 13.2

• 132

Multiple Choice

10.2x8=

• 8.16

• 81.6

• 816

Multiple Choice

33.2x4=

• 13.28

• 132.8

• 1328

• 13280

Multiple Choice

Each math text book weights 1.2 pounds. How much do 32 math books weigh?

• 33.2 pounds

• 38.4 pounds

• 384 pounds

Multiple Choice

Michael purchases 12 pencils at the school bookstore. They cost $0.35 each. How much did he spend on pencils?

• $3.23

• $2.80

• $4.20

• $30.00

Multiple Select

When multiplying decimals do we have to line the decimal up?

• Yes always

• No not when multiplying