lunes, 4 de agosto de 2008

Maths is Fun

Maths Is Fun
Explore primary and intermediate math, solve puzzles, and play games.

Enter in the Numbers section. You can work with numbers, its basic operations, fractions, decimals, percentages...

Try the Algebra section. It's very interesting and complete.
* Basic Operations and its order.
* Exponents
* Simplifying
* Linear Equations
* Quadratic Equations
* Polynomials
and much more.

Also there are puzzles, games...

domingo, 11 de noviembre de 2007

Rounding numbers

How to round numbers
  • Make the numbers that end in 1 through 4 into the next lower number that ends in 0. For example 74 rounded to the nearest ten would be 70.
  • Numbers that end in a digit of 5 or more should be rounded up to the next even ten. The number 88 rounded to the nearest ten would be 90

  • You can round off a number in different ways: Example:
    to the nearest unit: 643,78 = 644,
    to the nearest 10 (ten) --> 643,78 = 640
    to the nearest 100 (hundred) --> 643,78 = 600
    to the nearest 1/10 (tenth) --> 643,78 = 643,8

    More interactive exercises:

    Transversal postulate: tranversal and parallel lines

    If a transversal intersects two parallel lines then:
    (a) All corresponding angles are equal. Angle1 = Angle5
    (b) Each pair of alternate angles are equal (congruent). Angle1 = Angle3
    (b) the interior angles on the same side of the transversal are supplementary. Supplementary angles are any two angles whose sum is 180 degrees. Angle1 + Angle2 = 180º

    Exercise: r line is parallel to s line. The angle1 measures 60 degrees.
    Find the measures of the other seven angles in the figure (right).

    Clic on the picture below to see a graphic proof.

    Angle2 = 120 degrees since it is supplementary to angle 1.
    Angle3 = 60 degrees since Angle1 and Angle3 are vertical angles.
    Vertical angles are two nonadjacent angles (opposite angles) formed by two intersecting lines.
    Angle4 = 120 degrees since it is supplementary to angle1.
    Angle5 = angle1 = 60º, by the Transversal Postulate.
    Angle6 = angle2 = 120º,
    angle7 = angle3 = 60º, and
    angle8 = angle4 = 120º, by the Transversal Postulate.

    (to) intersect = intersectar, cortar
    postulate= postulado, enunciado intuitivo que no se demuestra.
    (to) measure= medir
    proof= demostración

    sábado, 10 de noviembre de 2007

    You are a guess!

    You are with your favourite friends.
    Do you like impressing them?
    Use this easy number trick.
    1º- Tell someone of them to pick a two digit number.
    2º- Then tell them to add the digits, and subtract this sum from the original number.
    3º- Then tell them to add the digits of the result.

    Now, you will guess this result.
    Read the comment below (Comentarios) to know it

    domingo, 28 de octubre de 2007

    Divisibility rules

    Do you remenber divisibility rules? Review it here
    Is 2064 divisible by 6?
    Is 5 a factor of 75?
    Is 17 a prime or composed number?
    Write all factors of number 24.

    Exercises on divisibility (2º ESO)
    More exercises on divisibility (1º ESO)
    More exercises on divisibility

    A video about primes, factorization, divisibility...

    Order of operations

    Do you remember order of operations?
    1º: Parentheses,
    2º: Exponents,
    3º: Multiplication & Division,
    4º: Addition & Subtraction


    a) 13 - 5 · 2 + 6 =
    b) (13 - 5) · (2 + 6) =
    c) 32 x 43 =
    d) 9 x (5 + 3)2 - 144 =
    e) (3 + 2 ·(16 - 3·4) - 7) · 5 =

    Magic stars

    A magic star is composed of straight line segments.
    Every straight line segment has three points with three numbers.
    The sum of the three numbers in each segment is equal to a same number.
    So, in a five-pointed magic star you can see numbers from 0 to 14 and the the sum of three numbers in each segment always is 21.
    Exercises on five-pointed magic star

    In a seven-pointed magic star you can see numbers from 0 to 20 and the the sum of three numbers in each segment always is 30.
    Exercises on seven-pointed magic star

    These exercises are very good for increase your mental calculations.

    viernes, 26 de octubre de 2007

    Elections for Class representative

    A class of 32 students elects their delegate or representative (class rep). The winner got 5/8 of the vote. If all students voted, how many students voted for the winner?

    a) 16sometextb) 18sometextc) 20sometextd) 22 sometext Answer: 3 · 9 - 4 · 2 + 6 - 5

    For more fractions problems, see the following pages (tutorials online with oral english explanations):

    Prime factorization, GCF (Greatest Common Factor), LCM (Least Common Multiple), Decimals and fractions

    Adding and substracting fractions.

    Adding and substracting fractions and mixed numbers.

    Fraction operations: multiplyimg fractions and mixed numbers.

    Taken from

    All elementary Mathematics

    Lessons, study guide and some problems about Arithmetics, Algebra, Geometry...

    domingo, 21 de octubre de 2007

    Problems withs natural numbers (1)

    1- There can be 39 students in the Computer class. The class has 14 boys and 17 girls. How many more students can join the class?

    2- A pair of shoes cost $10 and a pair of sandals cost $8. What is the total cost of 3 pair of shoes and 4 pair of sandals?

    The big race

    Let’s suppose that Andrew and Charles run the 100 metres at a constant speed.
    When Andrew crosses the finish line, Charles has run only 95 metres.
    So Andrew wins the competition with a lead of 5 metres.
    During a second competition, Andrew (who wants to make the competition more “balanced”) , penalizes himself voluntarily , starting 5 metres back the starting-line.
    It is supposed that the two athletes run with the same speed they had during the first competition.
    Who will win the second competition?

    Men and T. Rex

    If the Tyrannosaurus Rex weighed seven tons and the average man
    weighs 164 pounds,
    how many men would it take to equal the weight
    of T-Rex?

    Remember: 1 pound = 0.4545 kg