Unit 3: Test 2 Add, Subtract, Multiply and Divide Decimals NBT.7 StudyGuide/Homework
Decimal Addition. You can use decimal models to help you add decimals. Add. 1.25 + 0.85
Step 1. Shade squares to represent 1.25
Step 2. Shade additional squares to represent adding 0.85.
Step 3. Count the total number of shaded squares. There are 2 whole squares and 10 one-hundredths squares shaded. So, 2.10
wholes in all are shaded.
So, 1.25 + 0.85 = 2.10
Now, you try. Draw a picture to show your work.
(1) 0.81 + 0.43
(2) 1.4 + 0.22
Decimal Subtraction. You can use decimal models to help you subtract decimals. Subtract. 1.85 – 0.65.
Step 1: Shade squares to represent
1.85.
Step 2: Circle and cross out 65 of the shaded squares to represent subtracting 0.65.
Step 3: Count the shaded squares that are not crossed out. Altogether, 1 whole square and 20 one-hundredths squares, or 1.20
wholes, are NOT crossed out.
So, 1.85 – 0.65 = 1.20
Now, you try. Draw a picture to show your work.
(3) 1.4 – 0.61
(4) 1.6 – 1.08
Example 1. Find the product.
0.7 x 0.4 = ⃝
Step 1. Use a 10 x 10 grid. Shade 0.7 of the columns of squares.
Step 2. Shade 0.4 of the rows of squares. The part that over laps is the product.
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Solution: There are 28 out of 100 squares, or 0.28, in the overlap. 0.7 x 0.4 = 0.28
5)
Find the product. Use the 10 x 10 grid to help you multiply. 0.9 x 0.5 = ⃝
(A) 0.05 (B) 0.4 (C) 0.45 (D) 0.5
6) Multiply. Use decimal models.
0.8 x 0.5 = ⃝
7) Multiply. Use the decimal model. 0.4 x 1.9 = ⃝
Find the product.
8) 3.59 x 4.8 = ⃝
9) 2.19 x 6.3 = ⃝
10) 15.98 x 61 = ⃝
11) 59.8 x 23 = ⃝
Example 1. You can use a decimal model to divide decimals. Find the quotient: 0.2 ÷ 5 = ⃝
Strategy: Use a model. Use a 10 by 10 grid. (1) Shade 0.2 of the model. (2) Use circles to separate the shaded
area into 5 equal groups. (3) Count the number of squares in each group. There are 4 squares in each group.
Four squares represents 4 hundredths, or 0.04.
Solution: 0.2 ÷ 5 = 0.04
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12) Find the quotient. Use the grid to help you divide. 0.4 ÷ 5 = ⃝
(A)
(B)
(C)
(D)
8
0.8
0.08
0.008
13) Divide. Use decimal models. 0.15 ÷ 0.03 = ⃝
Divide. You will have to add “imaginary zeros or place holders” in order to complete the answer. You will not
have remainders.
14)
97.3 ÷ 35 = ⃝
(A) 278
15) 7.8 ÷ 15 = ⃝
(A) 0.052
16)
49 ÷ 14 = ⃝
(A) 3.5
17) 1.14 ÷ 0.76 = ⃝
(A) 10.5
18)
7.59 ÷ 2.2 = ⃝
(A) 345
(B) 2.78
(C) 27.8
(D) 20.78
(B) 50.2
(C) 5.2
(D) 0.52
(B) 35
(C) 3.05
(D) 30.5
(B) 1.05
(C) 1.5
(D) 15
(B) 3.45
(C) 34.5
(D) 3.045