Lesson: Multiplying by Doubling and Halving

Comment on Multiplying by Doubling and Halving

I'm really enjoying these videos. Thanks!
gmat-admin's picture

Glad to hear you're enjoying them!

Great techniques. Thank you very much.
gmat-admin's picture

Thanks for that!

After this video, I had an "AHA!" moment lol, Thanks GMATPrep!
gmat-admin's picture

Good to hear!

Thank you

very cool, thanks

Very good and simple technique..
I liked it very much and it is very easy..
Thank you very much for explaning this technique..

nice .. i am gaining confidence step by step...

are the se all videos enough for decent scores as i dont want to waste my time on random resources ?
gmat-admin's picture

Yes, our course covers every concept and strategy necessary to beat the GMAT.

This is a great strategy!
Thanks!
Rashad046's picture

Although it has been more than 20 year ago, since I last sit math exams I do enjoy learning it againg with these videos
gmat-admin's picture

Glad to hear it!

Just to confirm this only works on products correct?
gmat-admin's picture

That's correct.

Euro's picture

good video

Alternatively, prime factorization for the numbers under the root =)
gmat-admin's picture

Yes, we could! That concept is covered later in the course, so I didn't discuss in this video.

These videos are such helpful! Wonderful job team. Kudos

Very easy and interesting techniques to learn

Why did I never knew this before? You're a genius! Thank you so much!

Wish they taught math in school this way :-) . thanks a ton! - Shiva

Another brilliant video!!

do you have slides for the video courses ?
gmat-admin's picture

We have 2 sets of flashcards (for GMAT math and GMAT critical reasoning) that are taken from slides of the course.
They can be found here: https://www.gmatprepnow.com/content/free-content

Cheers,
Brent

Not to sound stupid, but would this work under any circumstances for division?
gmat-admin's picture

Great question! I hadn't thought of that.

Since a ÷ b is the same as a/b, we can apply some nice fraction rules to division.
For example 17.5 ÷ 2.5 = (17.5)/(2.5)
Notice that we can take (17.5)/(2.5) and multiply top and bottom by 2 to create an EQUIVALENT fraction 35/5, which is much easier to evaluate.
So, 17.5 ÷ 2.5 = (17.5)/(2.5) = 35/5 = 7

So, if it helps us, we can take ANY division and multiply both parts by the same value to create an easier division.

Here's a quick one: 21/5 ÷ 7/5
If we multiply both parts by 5, we get: 21 ÷ 7, which is much easier to deal with.

Cheers,
Brent

Very helpful. Thank you so much :)

Add a comment

Office Hours

Have questions about your preparation or an upcoming test? Need help modifying the Study Plan to meet your unique needs? No problem. Just book a Skype meeting with Brent to discuss these and any other questions you may have. 

Change Playback Speed

You have the option of watching the videos at various speeds (25% faster, 50% faster, etc). To change the playback speed, click the settings icon on the right side of the video status bar.

Have a question about this video?

Post your question in the Comment section below, and I’ll answer it as fast as humanly possible.

Free “Question of the Day” emails!