by Linda

How to use the TI-84 Plus on the SAT for graphing!

SAT Official Question of the Day for 11/18, but do it MY WAY!

See the question here: http://sat.collegeboard.org/practice/sat-question-of-the-day?questionId=20141118&oq=1 The solution given on the SAT site (look at it, please) is soooo much harder than doing THIS! Go get your graphing calculator and read on…

Look at the choices:
a) -8
b) -4
c) 4
d) 8
e) 10

Try one. How about -8? So, we assume b = -8. Press ‘Y=’ on your TI-84 Plus (top left). Type into Y1: -2x^2-8x+5. That’s the function you get if you substitute -8 for b. Now press GRAPH (top right). (Do ‘ZOOM-6’ if you need a better picture.) What is the x-value of the highest point? It looks like about -2. The question says it should be 2. So, it’s not choice (a).

Try the next one: -4. Change Y1 (just type 4 over the 8), and press GRAPH again. This time it looks like the highest point is at x=-1. Still not right. It’s not choice (b).

Try 8. Change Y1 (just type +8 over the -4), and press GRAPH again. This time it looks like the highest point is at x=2. Choice (d) is correct.

And *THIS* is why I tell all of you to get the TI-84 Plus Graphing Calculator! Get one now: http://amzn.to/1tXyOTH

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11.17.14

by Linda

Distance, Midpoint, and Slope

This week’s topic has been Distance, Midpoint, and Slope.

Let’s go through that blue SAT book everyone has, http://amzn.to/1wADKLS, or http://amzn.to/1wtPZuD, and this ACT book for problems about distance, midpoint, and slope that can be solved using my TI-84 Plus programs DISTANCE. Sorry, I won’t post the actual problems here. But go dig out your books and calculator (buy them here: SAT, ACT , TI-84 Plus) and follow along.

SAT book

ISBN-13: 9780874478525. The page numbers included here are from that book, but if you have the other one (9780874479799), please refer to the Test number and Section number instead.

DISTANCE:

Test 1, Section 3, p. 397, problem # 6

Test 1, Section 3, p. 400, problem #15

Test 3, Section 8, p. 546, problem #10

Test 4, Section 6, p. 596, problem #10

Test 5, Section 8, p. 669, problem #8

Test 7, Section 3, p. 769, problem #4

Test 8, Section 3, p. 830, problem #2

Test 9, Section 5, p. 905, problem #8

Test 10, Section 2, p. 953, problem #17

ACT book

I’m working out of an older edition that only has 3 tests. I believe they are the same as the first 3 tests of the 2nd and 3rd editions. Once I have the newer book, I’ll add to this list.

DISTANCE:

Test 1, Section 2, problems #35, 45

Test 2, Section 2, problem #33

Test 3, Section 2, problems #38, 48

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11.07.14

by Linda

Slope

This week’s topic is: Distance, Midpoint, and Slope.

Q: The slope of the line passing through (-1,-3) and (7,y) is -1/2. What is the value of y?

Answer: -7

Algebraic solution by hand:

Use the slope formula:

Solution using my TI-84 Plus program DISTANCE:

Run DISTANCE. How?

Use your multiple choice answer choices. One of them is -7. (If you don’t have choices, draw a picture. Plot the point (-1,-3) and do a slope of -1/2 from there – down 1, right 2, down 1, right 2, … until you get to a point where x is 7. Read the y-value of that point – it will be -7 and check it using this program.)

x1=-1

y1=-3

x2=7

y2=-7

Ignore the distance information – we don’t need it for this problem. Press ENTER for the midpoint information, which we don’t need either. Press ENTER once more to find that the slope is -1/2.

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11.06.14

by Linda

Distance

This week’s topic is: Distance, Midpoint, and Slope.

Q: For what value(s) of x is the point (x,4) exactly 5 units away from the point (6,8)?

Answer: 3 or 9

Solution by hand:

Use the distance formula:

Solution using my TI-84 Plus program DISTANCE:

Draw a picture:

Guess that x=2, maybe. It’s probably an integer if this is an SAT problem. Use the answer choices if available.

Run DISTANCE. How?

x1=2

y1=4

x2=6

y2=8

The distance is 5.66. It’s too big – you wanted it to be 5 – so move the point a little closer to the middle.

Maybe x=3:

x1=3

y1=4

x2=6

y2=8

The distance is exactly 5. Perfect. (There’s also another possible answer, x=9. If you have multiple choice answers, you will see 3 and 9 as a choice, so try both and see that they both work. For a grid-in SAT problem, you would only have to find one answer anyway.) :

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10.30.14

by Linda

Ratios and Proportions

This week’s topic has been Ratios and Proportions.

Let’s go through that blue SAT book everyone has, http://amzn.to/1wADKLS, or http://amzn.to/1wtPZuD, and this ACT book for problems about ratios that can be solved using my TI-84 Plus programs RATIO and PROPORTN. (See these posts for examples: 10/27, 10/28, 10/29, 10/30)

Sorry, I won’t post the actual problems here. But go dig out your books and calculator (buy them here: SAT, ACT , TI-84 Plus) and follow along.

SAT book

ISBN-13: 9780874478525. The page numbers included here are from that book, but if you have the other one (9780874479799), please refer to the Test number and Section number instead.

RATIO:

Test 1, Section 7, p. 417, problem # 13

Test 4, Section 6, p. 594, problem #6

Test 10, Section 2, p. 953, problem #16

Test 10, Section 8, p. 980, problem #12

PROPORTN:

Math Multiple-Choice Sample Questions, p. 307, problem #6

Math Student-Produced Response Sample Questions, p. 347, problem #1

Test 1, Section 7, p. 417, problems # 11, 13

Test 2, Section 2, p. 452, problem #2

Test 3, Section 5, p. 528, problem #9

Test 3, Section 8, p. 543, problem #1

Test 4, Section 3, p. 583, problem #6

Test 5, Section 2, p. 639, problem #5

Test 6, Section 4, p. 715, problem #10

Test 7, Section 3, p. 768, problem #1

Test 9, Section 8, p. 916, problem #4

Test 9, Section 8, p. 918, problem #11

Test 10, Section 2, p. 950, problem #7

ACT book

I’m working out of an older edition that only has 3 tests. I believe they are the same as the first 3 tests of the 2nd and 3rd editions. Once I have the newer book, I’ll add to this list.

RATIO:

Test 2, Section 2, problem #15

PROPORTN:

Test 1, Section 2, problems #19, 39, 44

Test 2, Section 2, problems #3

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10.30.14

by Linda

Ratios

Q: Last month, the ratio of sunny days to rainy days was 3:2. How many rainy days were there last month, if the month had 30 days? (Assume all days were either sunny or rainy.)

Answer: 12

Solution by hand:

Number of sunny days = 3x

Number of rainy days = 2x

3x + 2x = 30

5x=30

x = 6

There were 2x rainy days, so there were 12 rainy days.

Solution using my TI-84 Plus Program RATIO:

Run RATIO. How?

Total number of items (days) = 30

Number of categories of items = 2 (sunny and rainy)

Ratio part for category 1 (sunny) = 3

Ratio part for category 2 (rainy) = 2

Distribution is: sunny = 18 and rainy = 12.

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10.29.14

by Linda

Proportions

Q: x is inversely proportional to w. If x = 6 when w = 8, what is x when w = 12?

Answer: 4

Solution by hand:

For inverse proportions, (x1)(w1) = (x2)(w2)

(6)(8) = (x)(12)

48 = 12x

x=4

Solution using my TI-84 Plus Program PROPORTN :

Run PROPORTN. How?

x1 = 6

y1 = 8 (here, we have renamed w1 as y1)

Have y2 (really w2)

y2 = 12

Choose ‘Inverse’ proportion.

Then, x2 = 4.

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10.28.14

by Linda

Proportions

Let’s change yesterday’s question around a bit:

Q: Wandering around blindly in a parking lot (don’t try it, please), the probability that the first car you bump into is blue is 2/5. If there are 500 blue cars, how many cars are in the parking lot?

Answer: 1250

Solution by hand:

Set up the proportion using the concept ‘blue / total = blue / total’:

2/5 = 500/x

2x = 2500

x = 1250

Solution using my TI-84 Plus Program PROPORTN :

Run PROPORTN. How?

x1 = 2 (blue)

y1 = 5 (total)

Have x2 (blue)

x2 = 500

Choose ‘Direct’ proportion (because it doesn’t say ‘inverse’ in the problem).

Then, y2 (the total) = 1250.

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10.27.14

by Linda

Ratios

Q: The ratio of blue cars to non-blue cars in the parking lot is 2:7. If there are 1260 cars in the parking lot, how many are blue?

Answer: 280

Solution by hand:

Number of blue cars = 2x

Number of non-blue cars = 7x

2x + 7x = 1260

9x=1260

x = 140

There are 2x blue cars, so there are 280 blue cars.

Solution using my TI-84 Plus Program RATIO:

Run RATIO. How?

Total number of items = 1260

Number of categories of items = 2 (blue and non-blue)

Ratio part for category 1 (blue) = 2

Ratio part for category 2 (non-blue) = 7

Distribution is: blue = 280 and non-blue = 980.

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10.26.14

by Linda

TI-84 Plus Programs

My TI-84 Plus programs are now available here. Instructions and examples for each of the 40 programs are there so you can learn how and when to use them. I’m in the process of cross-indexing them with the problems posted here. Check back often and ask me questions!

You know that SAT book everyone has? The blue one: This one, or this one. I’m about to start going through it page by page, pointing out the problems that can be solved using my programs. Stay tuned!

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Category Archives: TI-84 Plus

How to use the TI-84 Plus on the SAT for graphing!

SAT Official Question of the Day for 11/18, but do it MY WAY!

Distance, Midpoint, and Slope

This week’s topic has been Distance, Midpoint, and Slope.

SAT book

ACT book

Slope

Q: The slope of the line passing through (-1,-3) and (7,y) is -1/2. What is the value of y?

Distance

Q: For what value(s) of x is the point (x,4) exactly 5 units away from the point (6,8)?

Ratios and Proportions

This week’s topic has been Ratios and Proportions.

SAT book

ACT book

Ratios

Proportions

Q: x is inversely proportional to w. If x = 6 when w = 8, what is x when w = 12?

Proportions

Let’s change yesterday’s question around a bit:

Q: Wandering around blindly in a parking lot (don’t try it, please), the probability that the first car you bump into is blue is 2/5. If there are 500 blue cars, how many cars are in the parking lot?

Ratios

Q: The ratio of blue cars to non-blue cars in the parking lot is 2:7. If there are 1260 cars in the parking lot, how many are blue?

TI-84 Plus Programs