multiplying decimals -...
TRANSCRIPT
Multiplying Decimals
Tuesday, September 16, 14
Using Base Ten Blocks
Ones - Whole Number Tenths
Hundredths
1 0.1 0.01
Tuesday, September 16, 14
A rectangular park measures 1.5 km by 2.3 km. What is the area?
2.3
1.5
Use Base Ten Blocks to build a rectangle with the length 2.3
and 1.5.Count the blocks in
the rectangle.
There are 2 flat blocks (2 ones) = 2 X 1 = 2There are 13 rods (12 tenths) = 13 X 0.1 = 1.3
There are 15 small cubes (hundredths) = 15 X 0.01 = 0.15The total area is: 2 + 1.3 + 0.15 = 3.45 km
Tuesday, September 16, 14
What is the value represented by each question below?
?
?
a) b) ?
?
Tuesday, September 16, 14
What is the value represented by each question below?
1.2
1. 3
a) b) 2.1
1.1
1 flat block (1 ones) = 1 X 1 = 15 rods (5 tenths) = 5 X 0.1 = 0.56 cubes (hundredths) = 6 X 0.01 = 0.06The total area is: 1 + 0.5 + 0.06 = 1.56
2 flat blocks (2 ones) = 2 X 1 = 23 rods (3 tenths) = 3 X 0.1 = 0.31 cubes (hundredths) = 1 X 0.01 = 0.01The total area is: 2 + 0.3 + 0.01 = 2.31
1.000.500.06+1.56
2.000.300.01+2.31
Tuesday, September 16, 14
A rectangular park measures 1.5 km by 2.3 km. What is the area?
You can also multiply using the method for multiplying whole numbers!
Step 1: Remove the decimal points from the factors to find the product.
Step 2: Count the decimal places in the factors and put the decimal back.
Step 3: Round to check using estimation!
15X 23 45 30x +345
1.5 -> 1 decimal place2.3 -> 1 decimal place
3.45 -> 2 decimal places
2X 2
4
Tuesday, September 16, 14
You can also multiply using the method for multiplying whole numbers!
a) 1.1 X 2.1b) 0.6 X 1.5c) 3.2 X 1.4d) 4.13 X 2.51
Tuesday, September 16, 14
You can also multiply using the method for multiplying whole numbers!
a) 1.1 X 2.11121x
11220+231
1.1 = 1 decimal place2.1 = 1 decimal place
2.31 = 2 decimal places
b) 0.6 X 1.515 6x
90
1.5 = 1 decimal place0.6 = 1 decimal place
0.90 = 2 decimal places
2.31 0.90
Tuesday, September 16, 14
You can also multiply using the method for multiplying whole numbers!
c) 3.2 X 1.43214x
128320+448
3.2 = 1 decimal place1.4 = 1 decimal place
4.48 = 2 decimal places
d) 4.13 X 2.51413 251x
4132065082600
4.13 = 2 decimal places2.51 = 2 decimal places
10.3663 = 4 decimal places
4.48 10.3663+103663
Tuesday, September 16, 14
rectangle model methodExample: 1 kg of grapes costs $2.95. How much would
1.8 kg of grapes cost?
2.0 x 1.0
2.0 x 0.8
0.95 x 1.0
0.95 x 0.8
2.95
1.8
Split each decimal into whole numbers
and remainders:2.95 = 2.0 + 0.951.8 = 1.0 + 0.80
Tuesday, September 16, 14
rectangle model methodExample: 1 kg of grapes costs $2.95. How much would
1.8 kg of grapes cost?
2.0 x 1.0
2.0 x 0.8
0.95 x 1.0
0.95 x 0.8
2.95
1.8
Split each decimal into whole numbers
and remainders:2.95 = 2.0 + 0.951.8 = 1.0 + 0.80
2.95 x 1.8 = (2.0 x 1.0) + (0.95 x 1.0) + (2.0 x 0.8) + (0.95 x 0.8)(2 x 1) + (0.95 x 1) + (2 x 0.8) + (0.95 x 0.8) =
= (2) + (0.95) + (1.6) + (0.76) = 5.31
= 2
= 1.6
= 0.95
= 0.76
Tuesday, September 16, 14
Multiplying Decimalspractice
Pg. 102 #1, 2, 4, 5
Tuesday, September 16, 14