↑ Return to Number Sense Video Lessons

↑ Return to Number Sense Video Lessons

Page 6- Add to 10 Tens Digit

Page 7 – Multiplying by 25

Page 8 – Multiplying by 50

Page 9 – Multiplying by 75

Page 10 – Multiplying by 125

Page 11 – Multiplying by 11

Page 12 – Multiplying by 111

Page 13 – Multiplying by 12

Page 14 – Multiplying by 15

Page 15 – Multiply by 16 2/3

Page 16 – Multiplying by 101

Page 17 – Multiplying by 1001

Page 18 – Multiplying both over 100

Page 19 – Multiplying both under 100

Page 20 – Multiplying over/under 100

Page 21 – Double/Half Multiplication

Page 22 – Double/Double Division

Page 23 – Adding/Subtracting Fractions

Page 24 – FOIL

Page 25 – Multiplying over/under square

## 47 comments

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## Bryan Neal

November 9, 2014 at 11:35 pm (UTC 0) Link to this comment

Hi there. Thanks for the number sense video resources/tricks. Using different platforms for students to learn this year has been a new thing I have been searching for. Thanks so much.

Bryan Neal

## S.C.

April 9, 2015 at 12:30 am (UTC 0) Link to this comment

Thank you for these awesome tricks. You are very thoughtful for posting these videos on top of being a teacher and teaching your own students. My score has increased magnificently. Thank you so much!

## anthony gillespey

April 28, 2015 at 7:59 pm (UTC 0) Link to this comment

Your welcome, I’m going to start working on a Calculator book and video series sometime this summer.

## Lightning

May 29, 2015 at 10:02 pm (UTC 0) Link to this comment

Hello. I was wonder if there was a trick for multiplying 43×34 or 67×76. Like a reflection trick. Thank you.

## anthony gillespey

June 8, 2015 at 4:58 pm (UTC 0) Link to this comment

I don’t know of one although Ill spend sometime on the Algebra and see if i can find something.

## Math Rocks

April 26, 2016 at 11:50 pm (UTC 0) Link to this comment

u can use foil

## anthony gillespey

June 9, 2015 at 7:32 pm (UTC 0) Link to this comment

Just changed the formatting for the pages with videos. Each video now has its own page. I had a problem with the plugin I used for the page and had to change it a bit. Let me know if anyone sees mistakes.

## Adhav

October 10, 2015 at 1:52 am (UTC 0) Link to this comment

Is there a shortcut to this problem?

If there is can you help me solve this problem.

9 2/15 – 5 4/5 = ?

Thank you

## anthony gillespey

October 20, 2015 at 9:48 pm (UTC 0) Link to this comment

Not really for this one. Just crunch the numbers like normal.

## Math Rocks

April 26, 2016 at 11:50 pm (UTC 0) Link to this comment

What I did when I saw that question on the MSNS was I did 4/5 and made that 12/15. Then, I subtracted 12/15 from 2/15. I did this by going up from 12 to 15 (add 3) and then I added 2 to get 1 and 2/15. I added 5/15 to 12/15 to get to (1 and) 2/15. 5/15 simplified is 1/3. Then, since I went UP 5/15 to solve for the fraction, I did 9-5, which is 4, but since I went UP to simplify the fraction, I subtracted 1 more time, to get 3 and 1/3 as my answer. This probably won’t even make sense to you, but if it does, I hope it works later in the future. It’s easier to explain it visually.

## Adhav

June 11, 2016 at 3:08 pm (UTC 0) Link to this comment

Thanks

## anthony gillespey

April 27, 2016 at 1:11 am (UTC 0) Link to this comment

Another interesting way is to be OK with negative answers. 9-5=4 and 2/15 – 4/5 = 2/15 -12/15 = – 10/15 so you get 4 and – 2/3 or 3 and 1/3. Which is nice since the numbers stayed small.

## Adhav

June 11, 2016 at 3:09 pm (UTC 0) Link to this comment

Thanks

## Jake

October 22, 2015 at 1:36 am (UTC 0) Link to this comment

Is there an easy way to multiply a 3 digit number by another 3 digit number

Ex:

565*344

## anthony gillespey

October 26, 2015 at 1:18 pm (UTC 0) Link to this comment

Are you doing Number Sense Tests? If so I think you are doing an estimation question. If that is the case you dont really care what the exact answer is. If I was doing this question you asked with estimation then is alot easier. 565*344 is really close to 560 * 333. which would be 560 *1/3 with some zeroes. Which is really easy.

## Mia hinojosa

November 9, 2015 at 2:09 am (UTC 0) Link to this comment

Hey do you know the 33 1/3 trick I could not find it in your book?

## anthony gillespey

November 13, 2015 at 7:10 pm (UTC 0) Link to this comment

33 and 1/3 is basically 1/3 think of it as 1/3 and do the math then figure out how many zeroes to add.

## Math Rocks

January 6, 2016 at 1:20 am (UTC 0) Link to this comment

Hello. On the Cross Timbers Number Sense Test on October 2015, there was a question (question 76) that I didn’t know any trick for. It wasn’t an estimation question either, so I was wondering how to do it. The question was, 143 x 133. Can you tell me how to solve this if there is a way to? Thanks.

## anthony gillespey

January 16, 2016 at 3:55 am (UTC 0) Link to this comment

I’ll give you a hint 143 is a multiple of 7.

## Math Rocks

January 23, 2016 at 3:15 am (UTC 0) Link to this comment

Thanks. I saw it on page 28

## Adhav

January 11, 2016 at 1:16 am (UTC 0) Link to this comment

is there a trick for multiplying 213 by 138?

## Math Rocks

March 1, 2016 at 12:11 am (UTC 0) Link to this comment

I don’t know if this will help, but I found that 213 = 71 x 3, and 138 = 23 x 6, or 23 x 2 x 3.

## anthony gillespey

March 2, 2016 at 2:02 pm (UTC 0) Link to this comment

I discovered those myself not to long ago. I think in later editions of the book I will include those. Thanks.

## Math Rocks

February 19, 2017 at 8:46 pm (UTC 0) Link to this comment

you should round 138 to 140 and 213 to 200

## Math Rocks

April 20, 2016 at 1:17 am (UTC 0) Link to this comment

Well, Flour Bluff has dominated once again. I’m from Fowler, and we got 3rd place. I can’t understand how Flour Bluff could get 5100 points! They’re so good, but next year our school will probably be moved down to 4A because there is a new school coming in. But anyways, I’ll get to the point. Mr. Gillespy, I have a question for you about the recent state test. How do you number 53, which states A set with 10 elements has how many 7-element subsets? BTW, I got 5th place in Number Sense!

## anthony gillespey

April 20, 2016 at 1:29 pm (UTC 0) Link to this comment

Fowler did really good this year. You guys gave us a run for our money and should be extremely proud of your results. Having you guys in 5A definitely makes the contest more exciting.

Great job getting 5th at state I know that was incredibly hard to do. hopefully my book helped.

To answer your question about question 53, subsets with certain amounts are just variations of Combinations so just think of it as a 10 choose 7 combination which is 10!/ (7! x 3!)

## Math Rocks

April 25, 2016 at 3:54 am (UTC 0) Link to this comment

Thanks Mr. Gillespy. Your book helped a lot too. I just have one more question. How do you solve this: The slope of a line with x-intercept of (5, 0) and a y-intercept of (0, –2) is?

## anthony gillespey

April 27, 2016 at 1:04 am (UTC 0) Link to this comment

What are you asking.? The slope or the equation of the line?

## Math Rocks

May 30, 2016 at 5:34 pm (UTC 0) Link to this comment

slope

## Math Rocks

January 29, 2017 at 5:50 pm (UTC 0) Link to this comment

never mind… I made a simple mistake while trying to do y1-y2/x1-x2

## Math Rocks

April 26, 2016 at 11:41 pm (UTC 0) Link to this comment

We might not be in 5A next year, because there is a new high school coming in next year, and it will probably lower the population which might place us in 4A. Can you answer the question I asked you?

Thx

## Lightning

December 20, 2016 at 6:18 pm (UTC 0) Link to this comment

Can u please make a calculator section tricks to ur website. I have a bit of trouble with it.

## anthony gillespey

January 12, 2017 at 8:10 pm (UTC 0) Link to this comment

Someday I will get around to it. Not ready to do that just yet.

## Math Rocks

February 15, 2017 at 3:11 am (UTC 0) Link to this comment

Hi Mr. Gillespy,

How do you do a problem like a times b/c. An example is 16 x 19/21. I know you can do it in your head but I was wondering if there was a fast way

## Math Rocks

February 15, 2017 at 3:13 am (UTC 0) Link to this comment

Hi Mr. Gillespy,

How do you do a problem like a times b/c. An example is 16 x 19/21. I know you can do it in your head but I was wondering if there was a fast way

## Math Rocks

February 18, 2017 at 12:02 am (UTC 0) Link to this comment

sorry for commenting the same comment two times, my computer was facing some problems and I think I double clicked the send button for the comment

## anthony gillespey

March 21, 2017 at 10:03 pm (UTC 0) Link to this comment

This problem is actually pretty hard to explain but ill give it a try. the key is that the denominator is 21. Subtract 19 and 16 from 21. You get 2 and 5. Multiply those numbers.

That is your new numerator. Your whole number is like the old trick. Since 19/21 is less than 1 you subtract the difference from 16. So the final answer is 14 10/21 . This gets harder when you multiply the numbers and they are negative. Look for this trick in my new book.

## Jacob

November 9, 2017 at 12:54 pm (UTC 0) Link to this comment

Thanks so much for making this book. Our school Vandeventer benefits from it a lot!

## anthony gillespey

November 13, 2017 at 7:39 pm (UTC 0) Link to this comment

Great to hear. Have a great season.

## NK

February 8, 2018 at 11:15 pm (UTC 0) Link to this comment

does any of this help if you are taking the PSAT 8/9?

## anthony gillespey

February 15, 2018 at 10:34 pm (UTC 0) Link to this comment

Some of it. General Math and Calculator would help more.

## NK

September 9, 2018 at 2:20 pm (UTC 0) Link to this comment

This will help for math and science team, right?

## MP

September 29, 2018 at 3:29 pm (UTC 0) Link to this comment

I was wondering if there was a trick for things like 1+2+3…+15=.

## anthony gillespey

October 3, 2018 at 12:16 pm (UTC 0) Link to this comment

yep its in the book and videos.

## FORTNITE

November 19, 2018 at 9:16 pm (UTC 0) Link to this comment

So, the double/double division trick is basically that since you have doubled both numbers when you divide it it comes out to the same number as the original equation, right?

## anthony gillespey

December 31, 2018 at 9:19 pm (UTC 0) Link to this comment

yep

## Smiley

January 29, 2019 at 1:39 am (UTC 0) Link to this comment

This is really helpful math and science learned alot