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Finding multiples to 100:

• Print and hand out the hundred boards worksheets attached to students.

• Have the students cross out multiples on their worksheet as you highlight them on-screen on

the Scrolling Hundred Board app. (See sheet at end of file.)

• Select 1 to start the hundred board.

• Click the Options button.

Select the even numbers (2x)

from the pop-out panel.

• Click and hold on the Pen button.

Select a shade from the pop-out

selection box.

• Circle the first multiple “2”

• Select the pointer

• Then click on the hide tool.

• Hide every multiple of 2 that is

highlighted EXCEPT the circled 2.

Finding Multiples and Prime Numbers

Select

Pop-out panel: select to highlight multiples

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• Click the options button, select “3x”. Circle the “3”

using the pen again.

• Select the pointer

• Then select the Hide tool and click to hide

all the multiples of 3.

• N.B. The hide function acts as a toggle: if you

click a cell with a hidden numeral, it will show it

again.

• Repeat steps for multiples of 5:

• Repeat steps for multiples of 7:

• Ask the students “thinking questions” as you go:

∗ “Why are all the multiples of 4 already crossed out?”

∗ “What about the multiples of 6, 8, 9 and 10?

Finding Multiples and Prime Numbers 2

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Identifying the prime numbers:

• With a purple pen, circle those that

are still visible (not hidden):

• Ask students, “What do you know about them?” “Why are they still showing?” “Why are they

different?”

• Explain that there are no factors for these numbers, except for 1 and the number itself.

• They are called “prime numbers”.

• Use the Options function to select “P” (prime) to highlight the

prime numbers. All the numbers that were circled are

highlighted.

• Point out the “1”. It is a special case because it has just one factor. It is not prime nor composite. Circle it with green.

• Discuss the number zero. “0” is not included in this chart but if it was

would it be prime or composite? It is a special number too like “1”. So 1

and 0 are neither prime nor composite.

Challenge questions:

• “Why do we not need to mutliples beyond 10x on a hundred grid?”

• Look at the prime numbers with odd numbers highlighted.

Why are all the prime numbers except 2 also odd numbers?

Finding Multiples and Prime Numbers 3

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Alternative Method Using Crossing Out:

Finding multiples to 100:

• Print and hand out the hundred boards attached to students.

• Have the students cross out multiples on their worksheet as you highlight them on-screen on

the Scrolling Hundred Board app.

• Click and hold on the Pen button.

Select a shade from the pop-out

selection box.

• Click the Options button.

Select the even numbers (2x)

from the pop-out panel.

• Circle the first highlighted

numeral, “2”:

• Select a different shade, cross out

every other multiple of 2:

Finding Multiples and Prime Numbers

Select

Pop-out panel: select to highlight multiples

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Finding Multiples and Prime Numbers

• Click the options button, select “3x”.

• Select the Pen tool. Circle the “3” ‘using one shade, Cross out the multiples of 3 using a

second shade:

• Repeat for multiples of 5:

• Repeat for multiples of 7:

• Ask the students “thinking questions” as you go:

∗ [Highlight the mulitiples of 4] “Why are all the multiples of 4 already crossed out?

∗ Repeat for multiples of 6, 8, 9 and 10

∗ [Challenge question] “Why do we not need to go beyond 10x?”

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Finding Multiples and Prime Numbers

Identifying the prime numbers:

• With a blue pen, circle those that

are not ruled out:

• Ask students, “What do you know about them?” Why are they different?

• Explain that there are no factors for these numbers, except for 1 and the number itself.

• They are called “prime numbers”.

• Identify tricky primes that have only themselves and one as factors (e.g. 2, 3 etc have only

itself and one but is shaded already). Select a purple pen and have students circle them too.

• Use the Options function to select “P” to highlight the prime numbers.

• Point out the “1”. It is a special case because it has just one factor. It is not prime nor

composite. Circle it with green.

• Discuss the number zero. “0” is not included in this chart but if it was would it be prime or

composite? It is a special number too like “1”.

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• Clear the screen and remove all pen marks

• Select P for prime. Then scroll forward one hundred by clicking

the double (hundred) down arrow.

• Continue clicking the hundred down arrow and noting the primes

as you go.. “Do they ever stop?” (no)

• Challenge questions: “Are there more or fewer primes, or the

same number on each page as the numbers get larger?” (less to

start with then it varies between 12 and 16 per page)

• Count them per page. (25 p1, 21 p2, 16 p3, 16 p4, 17 p5, 14 p6,

16 p7, 14, p8, 15 p9, 14 p10, 16 p11, 12 p12, 15 p13, 11 p14,

17 p15, 12 p16, 15 p17, 12 p18, 12 p19, 13 p20. This is as far

as the program will show. “Is there a pattern?” “Do you think the

prime numbers ever stop?”

• Explain that this is part of mathematics that has been investigated for hundreds of years.

Mathematicians have found that primes cannot be predicted and never cease. There are an

infinite number of prime numbers.

For even more advanced students:

Show these YouTube clips, for more fun with primes:

• https://www.youtube.com/watch?v=Jhp_XFMvHDA

• https://www.youtube.com/watch?v=iFuR97YcSLM

Challenge activity / Advanced activity: “Is there a pattern to prime numbers?”

7 Finding Multiples and Prime Numbers

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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

51 52 53 54 55 56 57 58 59 60

61 62 63 64 65 66 67 68 69 70

71 72 73 74 75 76 77 78 79 80

81 82 83 84 85 86 87 88 89 90

91 92 93 94 95 96 97 98 99 100

1 Finding Multiples and Prime Numbers

Shade in the cells as the multiples are identified. Remember not to shade those numbers that have only one and itself as factors (the first multiple in any set.)