"La mayor parte de las ideas fundamentales de la ciencia son esencialmente simples, y deben, como regla, ser expresadas en un lenguaje que cualquiera pueda comprender".
A. Einstein

jueves, 28 de noviembre de 2013

Primes and composites. Sieve of Erathostenes

This morning we studied what Primes and Composites are. Here you have the definitions.

The Sieve of Eratosthenes is an ancient method for finding all primes numbers up to a specified number.

It was created by Eratosthenes (275-194 B.C., Greece), an ancient Greek mathematician. Just as a sieve is a strainer for draining spaghetti,  Eratosthenes's sieve drains out composite numbers and leaves prime numbers behind. The numbers from 1 to 100 are listed in a table. We will  use The Sieve of Eratosthenes to find all primes up to the number 100 by following the directions below.

Directions:
  1. Cross out 1 since it is not prime.
  2. Circle 2 because it is the smallest prime number. Cross out every multiple of 2.
  3. Circle the next open number, 3. Now cross out every multiple of 3.
  4. Circle the next open number, 5. Now cross out every multiple of 5.
  5. Circle the next open number, 7. Now cross out every multiple of 7.
  6. Continue this process until all numbers in the table have been circled or crossed out.
You have just circled all the prime numbers from 1 to 100!

Download presentation


Questions (to be answered as a comment):

1. How many prime numbers are there from 1 to 100?
2. List all prime numbers from 1 to 100.
3. Which number is the only even prime number?
4. An emirp (prime spelled backwards) is a prime that gives you a different prime when its digits are reversed. For example, 13 and 31 are emirps. List all emirps between 1 

Enjoy it.

domingo, 17 de noviembre de 2013

Fractions and decimals

Hi boys and girls,

here I post you a document about changing fractions to decimals and decimals to fractions. I hope you find it interesting and useful (See document).

Take care.

ALICIA