Page 45 - NUMINO_WB_5A
P. 45
099-P1-1
Prime Numbers
A number that has exactly two factors, 1 and itself, is called a prime number. Find
all the prime numbers from 1 to 50.
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
Step 1. Since 1 is not a prime number, cross it out. All the multiples of 2 have 2
as one of their factors. Cross out all the multiples of 2 except 2, since 2
has 1 and itself as its only factors.
Step 2. All the multiples of 3 have 3 as one of their factors. So, they are not
prime numbers. Cross out all the multiples of 3 except 3, since 3 has 1
and itself as its only factors.
Step 3. In the same way, cross out all the multiples of 5 except 5.
Step 4. Similarly, cross out all the multiples of 7 except 7.
Step 5. The number remaining after Step 4 are all prime numbers. Write all the
prime numbers from 1 to 50.
Prime Numbers
A number that has exactly two factors, 1 and itself, is called a prime number. Find
all the prime numbers from 1 to 50.
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
Step 1. Since 1 is not a prime number, cross it out. All the multiples of 2 have 2
as one of their factors. Cross out all the multiples of 2 except 2, since 2
has 1 and itself as its only factors.
Step 2. All the multiples of 3 have 3 as one of their factors. So, they are not
prime numbers. Cross out all the multiples of 3 except 3, since 3 has 1
and itself as its only factors.
Step 3. In the same way, cross out all the multiples of 5 except 5.
Step 4. Similarly, cross out all the multiples of 7 except 7.
Step 5. The number remaining after Step 4 are all prime numbers. Write all the
prime numbers from 1 to 50.
