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 TOPICS This page:   discrete math    Search   Dr. Math See also the Dr. Math FAQ:   permutations and   combinations Internet Library:   discrete math HIGH SCHOOL About Math Analysis Algebra    basic algebra    equations/graphs/      translations    linear algebra    linear equations    polynomials Calculus Complex Numbers Calculators/    Computers Definitions Discrete Math    permutations/    combinations Exponents    Logarithms Fibonacci Sequence/   Golden Ratio Fractals Functions Geometry    Euclidean/plane      conic sections/        circles      constructions      coordinate plane      triangles/polygons    higher-dimensional      polyhedra    non-Euclidean    practical geometry    symmetry/tessellations History/Biography Interest Logic Negative Numbers Number Theory Physics/Chemistry Probability Projects Puzzles Sequences/Series Sets Square/Cube Roots Statistics Transcendental   Numbers Trigonometry Browse High School Discrete Math Stars indicate particularly interesting answers or good places to begin browsing. Selected answers to common questions:     Four-color map theorem.     How many handshakes?     Squares in a checkerboard.     Tournament scheduling.     Venn diagrams. Question on a Math Counts Test [8/13/1995] Find the integral solutions to 1/x + 1/y = 1/7. A Quick Overview of P vs. NP Problems [11/19/2007] Can you explain what P and NP problems are at a level that a high school student can understand? Ramsey's Theorem and Infinite Sequence [06/01/1999] Ramsey's Theorem applied to divisibility in infinite sequences. Rat Population [04/27/1999] Estimate the number of offsping produced from a pair of rats in one year... Recursive and Explicit Formulas [01/19/1999] Is there an easy way to convert recursive formulas into explicit ones and vice versa? Resources for NIM [07/03/1997] Where can I find information about the game of NIM? Reversed Digits Theorem [06/24/1999] For a positive integer abc..., if (abc...)^n = xyz... and if (a+b+c+...)^n = x+y+z+..., how can I prove that (...cba)^n = ...zyx? Rock, Paper, Scissors [03/29/2001] If three people are playing Rock-Paper-Scissors, how many different combinations can be made, assuming order doesn't matter? Rubik's Cube Combinations [04/11/2001] I read that a rubics cube has 4 quintillion different possible combinations. Is this number correct? How can I calculate this value on my own? Segmenting Paths [08/20/1998] A path between opposite vertices of the square is made up of hundreds of horizontal and vertical segments. What is the best approximation to the length of the path - 24, 34, 44, or more than 44? Set and Element Relations [03/23/2003] On a set of n elements, how many relations are there that are reflexive and antisymmetric? irreflexive and symmetric? Set Equality [10/12/1998] Can you help me show that (A-B)-C = (A-C)-(B-C), where A, B, and C are sets? Sets and Integer Pairs [6/10/1996] A) Prove that the sum of a specified element of one set is greater than or equal to a specific number (n + 1)/2; B) Find all the ordered pairs of integers (m, n) that satisfy the equation (n^3 + 1) / (mn - 1). The Seven Bridges [8/28/1996] What is the problem from the 1700s about a town with seven bridges, where you want to cross each bridge exactly once? Showing Divisibility [07/12/1998] How do you show that 5^(2n) + 3(2^(2n+1)) is divisible by 7? Simple Proof by Induction [08/27/1999] How can I show by mathematical induction that the proposition "if n >= 1 then 3n >= 1 + 2n" is true? Solving a System of Modular Equations with Multiple Variables [12/15/2004] Thoughts on solving a system of modular equations such as: (1919ab) mod 5107 = 1 1919(a+1)(b-1) mod 5108 = 5047 1919(a+2)(b-2) mod 5109 = 1148 1919(a+3)(b-3) mod 5110 = 3631 1919(a+4)(b-4) mod 5111 = 2280 Subsets of Real Numbers and Infinity [08/22/2001] Am I correct in saying that both the whole number set and the integer set have an infinite number of numbers within them, and therefore are of the same size? Summation by Parts [01/07/2004] Using 'E' to represent sigma, is there an approximate solution to E(Ai*Bi) = ? where i = 0,1,...,n if Ai is known explicitly and E(Bi) is known? Sum of Reciprocals [08/05/2008] Find seven unique positive integers such that the sum of their reciprocals is 1. Sum of Squares of Two Odd Integers [10/26/1999] How can I prove that the sum of the squares of two odd integers cannot be a perfect square? Symmetric, Transitive, and Reflexive Relations [11/10/1998] Suppose R is a symmetric and transitive relation on A, and for each a in A there is b in A such that (a,b) and is in R. Show that R is an equivalence relation... System-Level Programming and Base 2 [05/03/2001] In computer programming, I have a result that contains several values, always a power of 2 (2^2, 2^3, 2^4). If my value is 2^3, 2^4, 2^6 304, how can I tell if 2^3 exists in 304? System of Equations and Gauss-Jordan [11/29/1998] Solve using the Gauss-Jordan method: a 5-percent solution of a drug is mixed with 15- and 10-percent solutions... Three Houses, Three Utilities [07/15/1999] Can you solve it using 2 dimensions? How? Three Number Theory Questions [10/25/1999] Find the sum of the digits in 4444^4444; find how many times the digit 1 occurs from 1 up to 10,000,000,000; find 3 integers greater than 5^100 that are factors of (5^1985)-1. Tiling with Dominoes [08/06/2001] A 6-square by 6-square board is tiled completely with 18 2x1 dominoes. Prove that at least one horizontal or vertical line can be drawn along the edges of the dominoes that divides the board into 2 regions, without cutting any dominoes in half. Total Membership [08/20/1999] At a country club 35 people play golf, 28 swim, and 24 play tennis. Of these, 6 play golf and tennis only, 9 play golf and swim only, and 7 play tennis and swim only. 8 people do all three. How many members are there altogether? Tracing a Figure Without Lifting Your Pencil [03/09/2001] Is there a simple way to quickly tell whether a figure can be traced without lifting your pencil? Traveling Salesman Problem [05/24/2001] Is there an easy solution to the "Traveling Salesman Problem"? Traveling Through a Square [11/25/2001] How do I get from the bottom left-hand corner of a 64-block square to the top right-hand corner, only going through each square once? Triangle in Randomly Colored Plane [10/28/2002] Prove: Assume that all points in the real plane are colored white or black at random. No matter how the plane is colored (even all white or all black) there is always at least one triangle whose vertices and center of gravity (all 4 points) are of the SAME color. Triangles within a Triangle [11/10/1996] If multiple small equilateral triangles are drawn within a larger one, what is the relation between the number of small triangles lying on the base of the big triangle and the total number contained within the big triangle? Types of Variables [01/14/1999] Can you explain the different types of variables, such as free variables and bound variables? Unions and Intersections: Proving Sets [10/17/1999] How can I verify a proof of the statement A - (B union C) = (A - B) intersect (A - C)? Unknown Numbers and a Venn Diagram [11/26/2001] The GCF of two numbers is 20 and the LCM is 840. One of the numbers is 120. Explain how to find the other number and use the Venn diagram method to illustrate. Using Graph Theory to Count Routes [07/15/1998] How do you use a diagram to count the number of different direct routes that connect five cities? Using Trees [10/18/1996] What are trees used for? What are some examples? Venn Diagram - Choose One of Three Options [01/24/1999] Members of a computer class choose at least one of three options. How many are taking just one? ... Use a Venn diagram. Venn Diagram: Goops, Gorps, Gorgs [09/19/2002] Every Goop is a Gorp. Half of all Gorgs are Gorps. Half of all Gorps are Goops. There are 40 Gorgs and 30 Goops. No Gorg is a Goop. How many Gorps are neither Goops nor Gorgs? Page: []

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