School Supplies
5.NBT.7
Did you know?
All of the strategies you learn are connected.
Today you will see how partial products is connected to the algorithm!!!
Solve 1.4 x 2.1 using the area model.
Estimate:
1x2=2
A little more than 2
Solve 1.4 x 2.1 using the area model.
1 x 2 = 2
.4 x 2 = .8 (.4 + .4)
1 x .1 = .1
.4 x .1 = .04
X
1
.4
2 .1
2 + .1 + .8 + .04 = 2.94
Debrief
Area model connected to partial products.
1.4
x2.1
.04
.4 x .1 = .04
.4 x .1 = .04
Area model connected to partial products.
1.4
x2.1
.04
.1
.4 x .1 = .04
.4 x .1 = .04
1 x .1 = .1
Area model connected to partial products.
1.4
x2.1
.04
.1
.8
.4 x .1 = .04
1 x .1 = .1
.4 x 2 = .8
Area model connected to partial products.
1.4
x2.1
.04
.1
.8
2
.4 x .1 = .04
1 x .1 = .1
.4 x 2 = .8
2 x 1 = 2
Area model connected to partial products.
1.4
x2.1
.04
.1
.8
2
2.94
.4 x .1 = .04
.4 x .1 = .04
1 x .1 = .1
.4 x 2 = .8
2 x 1 = 2
Connect partial products to the algorithm.
1.4
x2.1
14
280
2.94
The challenge here is where does the decimal point go?
Use your estimate.
1 x 2 = 2
The product will be a little more than 2.
Therefore the decimal point will go between the 2 and the 9.
All three strategies will work. Choose to use the strategy that is most efficient for you! Which strategy do you prefer?
Brain Break
.7
I know .7 goes in the rectangle.
.3 + .4 = .7
Fill in the rest of the empty rectangles.
Each box is the sum of the two boxes below. Complete the pyramid.
Answer key
It’s the end of the school year and the principal of Lisbon Elementary School has decided she will order all the school supplies for next year so that the teachers get an equal number of the supplies.
She looked at ads from two different stores, Discount Supplies and Office Den. She has budgeted $172 for each classroom and needs to find the best price.
Here is a list of supplies she needs to buy for each classroom:
What information do you need to know to help the principal decide what she can purchase?
The principal wants to purchase...
Item | Discount Supplies | Office Den |
Pens | $1.80 per box of 12. She needs to buy 7 boxes | $1.50 per box of 10. She needs to buy 8 boxes |
From which store should she buy?
Item | Discount Supplies |
Pens | $1.80 per box of 12. She needs to buy 7 boxes |
Calculate the price of 7 boxes from the Discount Supplies store.
1.8 x 7
Estimate first.
What will your cost be close to?
Estimated product for 1.8 x 7
NOTE: 1.80 = 1.8
Item | Discount Supplies |
Pens | $1.80 per box of 12. She needs to buy 7 boxes |
Calculate the price of 7 boxes from the Discount Supplies store.
1.8 x 7
Show your work. Use partial products, the area model, or the standard algorithm.
1.8 x 7 using the area model.
Item | Discount Supplies |
Pens | $1.80 per box of 12. She needs to buy 7 boxes |
Debrief: 1.8 x 7
1 x 7 = 7
.8 x 7 = 5.6
X
1
.8
7
7 + 5.6 = 12.6
1.8 x 7 using the area model. Partial Products
Debrief: 1.8 x 7
1 x 7 = 7
.8 x 7 = 5.6
X
1
.8
7
7 + 5.6 = 12.6
1.8
x7
5.6
7 .
12.6
.8 x 7 = 5.6
1 x 7 = 7
1.8 x 7 using the area model. Partial Products Algorithm
Debrief: 1.8 x 7
1 x 7 = 7
.8 x 7 = 5.6
X
1
.8
7
7 + 5.6 = 12.6
1.8
x7
5.6
7 .
12.6
.8 x 7 = 5.6
1 x 7 = 7
+5
1.8
x 7_
6
1.8 x 7 using the area model. Partial Products Algorithm
Debrief: 1.8 x 7
1 x 7 = 7
.8 x 7 = 5.6
X
1
.8
7
7 + 5.6 = 12.6
1.8
x7
5.6
7 .
12.6
.8 x 7 = 5.6
1 x 7 = 7
+5
1.8
x 7_
126
Estimate 7 x 2 = 14 a little less than 14
12.6 = 12.60
The total cost is $12.60
Item | Office Den |
Pens | 1.50 per box of 10 She needs to buy 8 boxes |
Calculate the price of 8 boxes from the Office Den store.
1.5 x 8
Estimate first.
What will your cost be close to?
Estimated product for 1.5 x 8
NOTE: 1.50 = 1.5
Calculate the price of 8 boxes from the Office Den. Show your work. Use partial products, the area model, or the standard algorithm.
Item | Office Den |
Pens | 1.50 per box of 10 She needs to buy 8 boxes |
1.5 x 8 using the area model.
Item | Discount Supplies |
Pens | 1.50 per box of 10 She needs to buy 8 boxes |
Debrief: 1.5 x 8
1 x 8 = 8
.5 x 8 = 4.0
X
1
.5
8
8 + 4.0 = 12
1.5 x 8 using the area model. Partial Products
Debrief: 1.5 x 8
1 x 8 = 8
8 x .5 = 4.0
X
1
.5
8
8 + 4.0 = 12
1.5
x 8
4.0
8 .
12.0
8 x .5 = 4.0
8 x 1 = 8
1.5 x 8 using the area model. Partial Products
Debrief: 1.5 x 8
1 x 8 = 8
8 x .5 = 4.0
X
1
.5
8
8 + 4.0 = 12
1.5
x 8
4.0
8 .
12.0
8 x .5 = 4.0
8 x 1 = 8
1.5 x 8 using the area model. Partial Products
Debrief: 1.5 x 8
1 x 8 = 8
8 x .5 = 4.0
X
1
.5
8
8 + 4.0 = 12
1.5
x 8
4.0
8 .
12.0
8 x .5 = 4.0
8 x 1 = 8
The principal wants to purchase...
Item | Discount Supplies | Office Den |
Pens | $1.80 per box of 12. She needs to buy 7 boxes | 1.50 per box of 10 She needs to buy 8 boxes |
How accurate was your prediction?
From which store should she buy?
The principal wants to purchase a few more items.
Help her decide how much each set of items will cost.
Practice Problem #1
Glue is $0.75 for 12 sticks. You can order half packs too.
You want to order 66 sticks. (5.5 packs)
What is the price of 5.5 orders of glue sticks?
Estimate first. Then, use an efficient strategy to solve.
Estimate:
Cost:
Practice Problem #2
3.6 x .25
Estimate first. Then, use an efficient strategy to solve.
Estimate:
Cost:
Practice Problem #3
.84 x 3.7
Estimate first. Then, use an efficient strategy to solve.
Estimate:
Cost:
Practice Problem #4
8.5 x 6.4
Estimate first. Then, use an efficient strategy to solve.
Estimate:
Cost: