RIC-0563 Developing algebraic thinking

PRIMES AND COMPOSITES
Teachers notes
More primes
More primes
involves using all 10 number tiles to create four primes—two
3-digit primes and two 2-digit primes. Other than using a calculator,
a ‘primeness check’ is a valuable tool on this task. Simply stated, the
check says: If any prime number less than or equal to the square root of
the given number divides the number, than the number is composite;
otherwise, it is prime.
Here are examples illustrating the ‘check’:
57 57 ≈ 7.55
Primes to check: 7, 5, 3, 2
57 is divisible by 3, so the number is composite.
589 589 ≈ 24.27
Primes to check: 23, 19, 17, 13, 11, 7, 5, 3, 2
589 is divisible by 19, so the number is composite.
203 229 ≈ 15.13
Primes to check: 13, 11, 7, 5, 3, 2
203 is not divisible by any of the numbers, so the number is prime.
1423 1423 ≈ 37.72
Primes to check: 37, 31, 29, 23, 19, 17, 13, 111, 7, 5, 3, 2
1423 is not divisible by any of the numbers, so the number is prime.
Here are possible solutions for the first activity.
601 201
47 53
283 467
59 89
The last activity is more difficult. It requires students to create five
different prime number using all 10 number tiles. There are no conditions
on the size of each number; however, the 0-tile cannot be placed in front
of a number, like 07. Here are some possible solutions:
2 47 61 83 509
5 23 41 89 607
3 5 67 281 409
R.I.C. Publications ® www.ricgroup.com.au DEVELOPING ALGEBRAIC THINKING 37
ISBN 978-1-74126-088-5