SAT Mental Math: Multiplying Tips | Video Post

One of the initial stumbling blocks in doing mental multiplication is you might forget that multiplying larger numbers requires breaking those larger numbers into more manageable pieces.

For instance, if you see 17 x 6, you might think I can’t multiply 17 times anything, except maybe one or two. But the thing is you don’t want to think of 17 x 6 as multiplying 17 times anything. I know, kind of crazy, right? But here’s how you do it:

Improve your SAT score; start your Magoosh SAT prep today

You break up 17 into two manageable numbers that you can both multiply times 6. Then, add the result of those two numbers to get the answer. Sure, you could 9 and 8, meaning (9 x 6) + (9 x 8), but the easiest way is to choose a number ending in a zero, since those numbers are easiest to multiply.

For example, 17 can be broken into 10 and 7. (Remember: 7 + 10 = 17). Multiplying the 6 by 10 should be pretty instantaneous: it equals 60. That leaves the 7, giving us 7 x 6 = 42. Adding those two gives us 42 + 60 = 102.

An important point is not to think of this as a writing exercise, in which you write 10 x 7 and 6 x 7. Multiplying these out the traditional way—pencil and paper—would work best. But when doing numbers in your head, breaking them up this way makes things a lot easier. What you are doing is multiplying the 10 x 6, then keeping that 60 “on hold”, while you multiply 6 x 7. Then you add that 60 to the 42.

What happens when you have a slightly larger number? Say 32 x 8?

One way would be to multiply 10 x 8 three times. But a faster way is to multiply 30 x 8, since 30 is a number ending in zero that is closest to 32. This gives us 30 x 8, which is the same as 3 x 8 with a zero at the end: 24, adding a zero at the end, gives us 240. We put this number “on hold” and then we multiply the 2 left over (remember, our original number was 32) times the 8: 2 x 8 = 16. We add this to the number “on hold”—240—giving us 240 + 16 = 256.

Check out the video for more SAT mental math practice!

By the way, Magoosh can help you study for both the SAT and ACT exams. Click here to learn more!

One Response to SAT Mental Math: Multiplying Tips | Video Post

  1. Math trainer June 13, 2017 at 5:45 am #

    I also recommend the Magoosh iOS app. The flashcards with an explanation of each problem are really helpful.


Magoosh blog comment policy: To create the best experience for our readers, we will only approve comments that are relevant to the article, general enough to be helpful to other students, concise, and well-written! 😄 Due to the high volume of comments across all of our blogs, we cannot promise that all comments will receive responses from our instructors.

We highly encourage students to help each other out and respond to other students' comments if you can!

If you are a Premium Magoosh student and would like more personalized service from our instructors, you can use the Help tab on the Magoosh dashboard. Thanks!

Leave a Reply