CPM Homework Help : CC3 Problem 2-77

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2-77.

Decide if each statement below is true or false. Explain how you know and name any properties you use. Refer to the Math Notes boxes in this lesson and in Lessons 2.1.5 and 2.1.7 to help you.

$-19+7=-7+19$
Hint (a):
Solve each side of the equation. Are they equal?
Answer (a):
This statement is false, because $-12\ne12$ .

$\frac { 4 } { 5 } \cdot 1 = \frac { 4 } { 5 }$
Hint (b):
Try using the Identity Property of Multiplication.
What does this property tell you about this statement?

$\frac { 3 } { 2 } \cdot \frac { 2 } { 3 } = 1$
Hint (c):
Do you remember what a multiplicative inverse is?
If not, refresh your memory using the glossary before approaching this problem.

$5\cdot7-5\cdot\frac{1}{5}=34$
Step 1 (d):
Simplify any terms with multiplication.
$(5)(7)-5\left(\frac{1}{5}\right)$
$35-1$
Step 2 (d):
Combine using subtraction, and then compare this value to $34$ .
Answer (d):
This statement is true, since $34=34$ .

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