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 />
Answer:

Step-by-step explanation:
Given
One-eighth times three-elevenths
Required
Solve
One-eighth means 1/8
Three-elevenths means 3/11
So, mathematically; the above expression is represented as thus:

To solve this, we simply multiply the numerator and the denominator together.
After multiplying these together, the next is to check if the resulting can be simplified
If yes,we simplify it and if otherwise, we live it like that.
So,



At this point, the fraction can't be simplified any further.
Hence,

Answer:
The function is decreasing in the following intervals
A. (0, 1)
C. (2, pi)
Step-by-step explanation:
To answer this question, imagine that you draw lines of slope m parallel to the function shown at each point.
-If the slope of this line parallel to the function is negative for those points then the function is decreasing.
-If the slope of this line parallel to the function is positive for those points then the function is increasing.
Observe in the lines drawn in the attached image. You can see that they have slope less than zero in the following interval:
(0, 1) U (2, pi)
Therefore the correct option is:
A. (0, 1)
C. (2, pi)
The answer is actually choice A
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If we add up the equations straight down we will have 0a+2b = 6
Note how adding the 'a' terms gives us 3a + (-3a) = 3a-3a = 0a. The 0a term is really 0 since 0 times anything is 0. So the 'a' terms will go away
The equation 0a+2b = 6 turns into 0+2b = 6 and that simplifies to 2b = 6
To isolate b, we divide both sides by 2
2b = 6
2b/2 = 6/2
b = 3
We can stop here since only one answer choice has b = 3, which is choice A. However, let's keep going to find the value of 'a'
Plug b = 3 into any equation with 'a' and 'b', then solve for 'a'
3a+4b = 9
3a+4*3 = 9
3a+12 = 9
3a+12-12 = 9-12
3a = -3
3a/3 = -3/3
a = -1
So a = -1 and b = 3 pair up to form (a,b) = (-1,3)
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To check, plug this ordered pair back into both equations
Equation 1:
3a+4b = 9
3*(-1)+4*3 = 9
-3+12 = 9
9 = 9
Equation 1 has been checked out
Equation 2:
-3a-2b = -3
-3(-1)-2(3) = -3
3 - 6 = -3
-3 = -3
this is true as well
So this confirms that the final answer is choice A