The Math Forum

Ask Dr. Math - Questions and Answers from our Archives
Associated Topics || Dr. Math Home || Search Dr. Math

Tricks for Solving Math Problems

Date: 9/27/95 at 23:50:19
From: Anonymous
Subject: Mathematical Tricks

I recently learned a trick for multiplying 2 digit numbers by 
11. Add the 2 digits of the number and insert the sum between 
the original 2 digits. If the sum is greater than 10, add the 
digit in the tens place to the original first digit.

Ex.  23x11 ->  2+3=5  => 253
     45x11 ->  4+5=9  => 495
     87x11 ->  8+7=15 -> 8+1=9 => 957

The theory shows up quickly when you manually calculate it 
out in longhand.

My question is, do you know of any other tricks like this 

I have seen TV ads for audio/video tapes promising to teach 
you tricks for multiplication, division & exponents.

Date: 10/10/95 at 21:41:58
From: Doctor Ethan
Subject: Re: Mathematical Tricks

	The most amazing book I have ever read regarding this is
Mathemagics by Benjamin and Shermer. It is great.

Also, you can get on a mailing list that will send you a new 
math trick every week.

You'll find an archive of its tips and other math tips and tricks at   

Hope this helps.

-Doctor Ethan,  The Geometry Forum

Associated Topics:
Middle School About Math

Search the Dr. Math Library:

Find items containing (put spaces between keywords):
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

Math Forum Home || Math Library || Quick Reference || Math Forum Search

Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.