## Thursday, June 05, 2014

### June 2014 Common Core Algebra 1 Regents Exam, Part 3

Update: I now have a Common Core Regents Review books available on Amazon.

This is the second thread dealing with the Common Core Algebra test, and probably the last for a while, as I'll be away from the weekend. The first thread was about Part 2 of the test. This post deals with part 3 and 4.

## Algebra 1 (Common Core), Part 3

Questions is Part 3 are worth four points. Again, I won't assume the point distribution for partial credit.

33. Write an equation that defines m(x) as a trinomial where m(x) = (3x - 1)(3 - x) + 4x2 + 19. Solve for x when m(x) = 0.

You need to multiply the binonials and then combine all the like terms.
(3x - 1)(3 - x) = 9x - 3x2 - 3 + x = -3x2 + 10x - 3
To that, add 4x2 + 19.
You get m(x) = x2 + 10x + 16. Don't forget to write it as an equation!

For the second part of the question, take the equation you found in the first part (they allow for consistent errors) and substitute 0 for x. The answer should be obvious, but I would still show the work -- especially because it says solve

m(0) = (0)2 + 10(0) + 16 = 0 + 0 + 16 = 16.

Frankly, I thought this problem was easier (or at least less complicated) than some of the Part 2 problems.

EDIT: As you may have seen in the comments below, in my rush to complete this section before leaving for the weekend, I misread my notes in solving this problem, despite having typed it correctly above. My original instinct was that this problem was too easy, and now I see why. Generally, when I get the feeling that something is too easy, there's usually something I missed, and I go look for it.

You needed to find when m(x) = 0, so x2 + 10x + 16 = 0. That's a simple quadratic equation to solve. What two factors of 16 add up to 10? That's 8 and 2.
So (x + 8)(x + 2) = 0
x + 8 = 0 or x + 2 = 0
Then x = -8 or x = -2.

So that would be a Conceptual error for this part of the question, which is more points off than a simple Computational error. It could have been worse. I might have been incredibly wrong and arrogantly displayed a lack of understanding of how functions work, but that would be entirely overstating the mistake made. In any event, I am told that some people like to make damning accusations under the guise of anonymity rather than step out into the light of day. But we don't talk about such things in polite company.

Now to continue.... End of EDITED SECTION

34. A rectangular garden measuring 12 meters by 16 meters is to have a walkway installed around it with a width of x meters, as shown in the diagram below (Note: This will be added later) Together the walkway and the garden have an area of 396 meters.

Write an equation that can be used to find x, the width of the walkway.

Describe how your equation models the situation.

Determine and state the width of the walkway, in meters.

Unlike the previous question, this was a majorly complicated problem, with more binomial multiplication.

The length of the rectangle is (2x + 16). The width of the rectangle is (2x + 12). The area of the rectangle is 396.

So (2x + 16)(2x + 12) = 396
4x2 + 24x + 32x + 192 = 396
4x2 + 56x - 204 = 0
x2 + 14x - 51 = 0
(x + 17)(x - 3) = 0
x + 17 = 0 or x - 3 = 0
x = -17 or x = 3

Discard the negative value and you are left with the width of the walkway being 3 meters wide.

Hopefully, that's enough.

35. Caitlin has a movie rental card worth \$175. After she rents the first movie, the card's value is\$172.25. After she rents the second movie, its value is \$169.50. After she rents the third movie, the car is worth \$166.75. Assuming the pattern continues, write an equation to define A(n), the amount of money on the rental card after n rentals.

Caitlin rents a movie every Friday night. How many weeks in a row can she afford to rent a movie using the rental card only? Explain how you arrived at your answer.

First, "Explain" means in words; equations will NOT be enough information. I am not kidding.

Subtract 175-172.25 and you get \$2.75. Check the next and the next to be sure, but you see that each rental is \$2.75
That makes the equation A(n) = -2.75n + 175.

To answer the second part, make an inequality greater than 0, and find the largest whole number which makes it true. (Or make an equation equal to 0 and drop everything after the decimal.)
-2.75n + 175 > 0
-2.75n > -175
n < 63.63
Each movie costs \$2.75 to rent. If you divide \$175 by \$2.75, you can get 63 rentals. There is money left over, but not enough for another rental using the card only.

36. An animal shelter spends \$2.35 per day to care for each cat and \$5.50 per day to care for each dog. Pat noticed that the shelter spent \$89.50 caring for cats and dogs on Wednesday.

Write an equation to represent to represent the possible numbers of cats and dogs that could have been at the shelter on Wednesday. Pat said that there might have been 8 cats and 14 dogs at the shelter on Wednesday. Are Pat's numbers possible? Use your equation to justify your answer. Later, Pat found a record sowing that there were a total of 22 cats and dogs at the shelter on Wednesday. How many cats were at the shelter on Wednesday?

This is a lot of work for a system of equations. I heard some teachers complaining about it (one of whom has seen the scoring rubric), and I heard students tell me that this was so easy. The students explained to me how they did it, so they might be correct in how "easy" they found it.

We'll use C for the number of cats and D for the number of dogs. That makes 2.35C the amount spent on cats and 5.50D is the amount spent on dogs.

The equation for Wednesday is 2.35C + 5.50D = 89.50.

For the second part, substitute 8 for C and 14 for D, and see if it's a true statement.

2.35(8) + 5.50(14) = 89.50 ?
18.80 + 77.00 = 89.50 ?
95.80 =/= 89.50 X

This is NOT a possible combination.

The final part states that C + D = 22. We now have a system of equations. Multiply this equation by -2.35

-2.35C + -2.35D = -51.70
2.35C + 5.50D = 89.50
combine: 3.15D = 37.80
divide: D = 12

There are 12 Dogs, so there are 22 - 12 = 10 = C, 10 Cats.

* * * * * * * * * * *

Okay, that's enough for me. This is taking a lot out of me.

What are your opinions of all this?

Anonymous said...

You seem to have gotten question 33 incredibly wrong. It's possible your arrogance got the best of you, or perhaps your understanding of functions is not as whole as you think. In any event I am told that if you get the answers wrong this test only takes 20 minutes.

(x, why?) said...

Feel free to offer your corrections and be part of the conversation. Or are you repeating what you've been told.

Anonymous said...

Uh, I think you found m(0) instead of setting m(x) = 0.

-Anon #2

(x, why?) said...

Yes, that's what I did. I was working from notes as I don't have a physical copy of the test. I'll have to correct that when I get home. Thanks for the correction. That makes more sense for them to ask.

Anonymous said...

Question #34
So x=3
But how do you make sure that you got the right answer?
Is there a way to check the answer if it's correct or not...?
I tried doing #34, and got x=3 same as you, but I am not confidence with my answer. I tried to check, but won't give me what I want.

tan

(x, why?) said...

The garden is 12 X 16. The walkway, x, is 3. That makes the length 3 + 12 + 3 = 18 and the width 3 + 16 + 3 = 22.

A = L * W = 18 * 22 = 396, which is what is stated in the problem.

I'm happy that you are concerned with checking your answers. Too many would get an answer and just move on. In a problem such as this one, it's easy to make a computation error along the way and not realize it.

Thanks for writing.

Unknown said...

For Q35, it asks how many weeks, not how many rentals needed

Unknown said...

For Q35, it asks how many weeks, not how many rentals needed

(x, why?) said...

She is renting 1 per week, so it is the same number.

Anonymous said...

for question 36, how did you get the 1st equation for the 3rd step

(x, why?) said...

The total number of cats plus the number of dogs is 22, so C + D = 22

We already know that it is \$2.35 to care for each cat and \$5.50 to care for each dog, and that Wednesday total was \$89.50, so 2.35C + 5.50D = 89.50.

We have a system of equations. To solve with elimination, we multiply the first one by -2.35 so that we can eliminate "C" and solve for "D" to find the number of dogs.

I hope this helps. Thanks for writing.

Anon 4 said...

you realize this conversation started three years ago right?

(x, why?) said...

Happens all the time, especially in December and May/June just before Regents exams.