The answer to 8a. is 17, the answer to 8b. is 3.9, the answer to 8c. is 1 / 2, the answer to 8d. is 7 7 / 8, the answer to 9a. is commutative property, the answer to 9b. is multiplicative identity property, the answer to 9c. is associative property, and the answer to 9d. is additive inverse property.
Regarding the whole "explain using mental math" thing, I pretty much just used the fact that 8a. and 8b. both had the same number of decimal places. For 8c., I just made each number have a denominator of 10. And last, for 8d., all of the denominators were already the same, which made it pretty easy. I apologize for this section of my answer being so informal lol, I haven't had to do these kinds of problems in like 5 years <span />
To make this a little clearer, let's give the pairs of inequalities the same denominator:
<span>Question 1:
</span>

?

First, apply the common denominator to the first fraction:

Do the same for the second:

Nest, compare the two fractions:

Therefore:

>

<span>
Question Two:</span>

?

Apply the common denominator to fraction one:

Fraction two:

Evaluate:

>

Therefore:
<span>
> 
</span>
Hope this helps!
To get a number to decrease by 21% you multiply it by 0.79 (1-0.21)
r = 0.79
Answer: y
=
x
2
+
93
x
−
288
Your Welcome
The second and the third one are similar.