Featuring 127 tricks with 146 examples! Last Updated: October 1, 2006 Welcome to Dr Numsen's Trick Center, your source for mental math tricks on the web, a part of Academic Meet Companion. The Trick Center provides mental math tricks used on the University of Texas Interscholastic League Number Sense Test and the Private Schools Interscholastic Association Number Sense Test. You need the Adobe Acrobat Reader to view and print the tricks. Search: WWW Academic Meet Companion Tricks Title School Elem/Mid/High Basics and Facts Everyone Should Know Subtracting Reverses EMH Divisibility and Remainders EMH Fractions, Percents, and Decimals EMH Prime Numbers EMH Order of Operations EMH Roman Numerals EMH Squares EMH Cubes and Other Powers MH Multiplication Tricks Multiplication by 14443 M+H Multiplication and Division by Powers of 10 EMH Multiplication by Multiples of Powers of 10 EMH Multiplication by 11 EMH Multiplication by 50 EMH Multiplication by 25 EMH Multiplication by 75 MH Multiplication by 125 MH Multiplication by 12 MH Multiplication by 111 MH Difference of Two Squares MH Multiplying Mixed Numbers with the Same Fraction E+MH Multiplying a times a/b MH Multiplying two numbers close to but greater than 100 E+MH Multiplying two numbers close to but less than 100 E+MH Multiplying two numbers with the same tens digits and whose ones digits add up to 10 E+MH Multiplication by 429 M+H Multiplication by 572 M+H Multiplication by 715 M+H Multiplication by 858 M+H Multiplying Multiples of Numbers Together MH Multiplying Two Digits Numbers Where the Ones Digits Sum up to 5 MH Advanced Arithmetic Changing from base 2 to base 4 MH Changing from base 2 to base 8 MH Changing from base b to base 10 MH Sum of Three Fractions in the form 1/(n)(n+1) + 1/(n+1)(n+2) + 1/(n+2)(n+3) MH Repeating Decimals MH Sequences and Series EMH Relatively Prime M+H Sum of Squares M+H Sums of Triangular Numbers M+H Finding Cube Roots of Large Numbers M+H Positive Integral Divisors -- 1 M+H Positive Integral Divisors -- 2 M+H Adding and Subtracting Fractions E+MH Summing Fibonacci and Fibonacci-like Sequences H Algebra Sum of the Roots of a Quadratic M+H Product of the Roots of a Quadratic M+H Patterns in f(x) M+H Slope M+H Geometry Squares, Rectangle, Circles, Triangles, Misc. Formulas E+MH Exterior and Interior Angles H The Diagonal of a Square M+H PSIA New Tricks for PSIA 2003 Number Sense M New Tricks for PSIA 2005 Number Sense M More Tricks to come!   + indicates an advanced trick for that level.