Page 198 - NUMINO TG_3A

12Beat the Calculator! Unit

CMath Vo abulary Associative Property of Multiplication: the grouping of factors does not change the product

2 . Multiply 3 numbers. 2. Have students use parentheses when
deciding the order in which to calculate the
Associative Property of Multiplication numbers.
The grouping of factors does not change the product. Example: 2a. 4 5 7
Method 1: (4 5) 7 20 7 140
(3 4) 2 = 24 3 (4 2) = 24 Method 2: 4 (5 7) 4 35 140
12 2 = 24 3 8 = 24 You can calculate faster if you use Method 1.

a. 4 5 7 = 140 b. 2 8 5 = 80 Have students understand that they need to
calculate the numbers inside the parenthesis
c. 3 4 5 = 60 d. 12 5 8 = 480 first.

e. 8 3 5 = 120 f. 6 7 5 = 210 3. In this exercise, students must find the
missing number in the multiplication sentence.

Now that students know the order in which
the numbers are multiplied does not change
the product, have them find the missing
number for each sentence.

3 . Find the missing number. b. 8 (3 2 ) = 48
d. ( 2 4) 7 = 56
a. (5 2) 4 = 40
12. Beat the Calculator! 113
10

c. (2 3 ) 6 = 36

Multiplying Three Numbers Using Arrays

You can draw arrays to show multiplication of three numbers. For example, show the first two factors (2, 5)
for 2 5 3 using arrays (rows and columns). Next, use the third factor, 3, to show how many two rows of
five there are, as shown below.

253

2 rows of 5 2 rows of 5 2 rows of 5

3A Unit 12 181