Powers, with a base of 2
Box for Powers of two:
- cubes and prisms
- coloured yellow, white, green
(small 1cm cubes for the follow up work)
prepared tickets for follow-up work
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Take a unit, ‘Here we have a unit, it is all on its own, it has no power.’, write a ticket, ‘1’
‘Now I am going to take my unit and put another unit with it’.
Move the unit to the right and place another unit to it’s side a unit - ‘Now it has a power’, write 2
‘I am going to replace it’, take the cuboid and check it on all sides, ‘So what did I have? I had one taken twice, I have two, we call this two to the first power’, flip the ticket and write 2 to the first power.
‘To go to the next power I take my two twice’. Move the built blocks to the right and add to the front. ‘I have a new power, two taken twice. Write 21 x 2 on the ticket. What did I do?, I have two taken twice, I have 2 to the second power’. Flip the note and write 22. ‘Do I have a piece to replace it with? , Yes I do’ Exchange it.
‘To go to the next power I take my two to the second power taken once twice’. Move the pieces to the right, Take the block, check it on all sides and place it in front of the pieces. Write 22 x 2 on the ticket, ‘I have a new power, two to the second power, taken twice, I have two to the third power’. Flip the note and write 23. ‘Do I have a piece to replace it with? , Yes I do’. Make the exchange,
‘To go to the next power I take my two to the third power twice’. Move the piece to the right first and then adding the other block to the side. Write 23 x 2 on the ticket, ‘I have a new power, two to the third power, taken twice, I have two to the fourth power’. Flip the note and write 24. ‘Do I have a piece to replace it with?, Yes I do’ Make the exchange.
Continue till you have a stack of two taken six times and have written the ticket.
How did I make that? What I did is I took two to the fifth power twice and move the original part to the ticket 25. Leave the other blocks and say, what did I do to get two to the fifth power? We took two to the fourth power twice, move the block of 24 over the ticket. Keep going till they are all replaced, put the extra unit on one side, the 26 ticket is left empty. Say, ‘I took my unit two twice to get to the first power. I can talk about my unit in terms of the power of 2, it is a unit to the zero power’. Take the ticket with ‘1’ written on it, reverse it and write ‘2 to the power of 0′.
To show the powers
This is a basic lesson with abstract ideas, therefore the lesson can be repeated many times. Children who grasp the concept can present to the others, it is given to children around the age of eight. It is sensorial, the ideas are abstract but the children are not being asked to abstract.
We make two to the power of six and then undo it to reinforce the work, it is how the power of zero is introduced.
The material follows the point. line, surface pattern established in the Wooden Hierarchical Material.
On another day, say to the children, ‘We call two the base and the little number is called the ‘exponent’, this comes from the Latin, ‘exponare’, which means to expand. We repeat the base the exponent number of times.’
The unit is always the building block, the first unit of each base is always the power of ‘0’, it has no group so it has no power.
To find the value you take the base the number of times of the value, e.g. 34 is 3x3x3x3
- The children discover that the unit is the base to the zero power.
- Children see a repetition of the geometric design (point, line and surface)
- Using the 1cm cubes shows that the size of the unit determines how far they can explore with the material.
- When moving from one power to the next power (e..g 21 x2 =22) you taken the power the base (21) number of times (x2)
When to give the lesson:
After the Wooden Hierarchical material with gives groups of ten, this work is presented soon after the work with squares and cubes of numbers and the notation.
Make the movements before writing the notation
After the lesson:
- The children repeat the presentation with the set of prepared tickets
- Encourage the children to record the values written on each side of the ticket, concentrating on the exponent first, e.g.
20 =1 =1
21 = 2 = 2
22 = 2×2 = 4
23 =2x2x2 = 8
24 =2x2x2x2 = 16
25 = 2x2x2x2x2 = 32
26 = 2x2x2x2x2x2 = 64
- Children can work with the 1cm cube, take a unit and say, ‘This has no power, If I put another unit with it it is two to the first power’, write the ticket,21. ‘To go to the next power I must taken this whole thing twice’, move the two units to the right, add the other piece. ‘Now I have my new unit which is two to the second power, it is two taken twice. Write a new ticket 22 and make the exchange. With the little box of cubes you reach the power of nine and can then deconstruct as before, finishing with the zero power as before. Now the power of nine is empty and the tickets are all shown.
Follow up work:
The powers using a base of three
Powers, using a base of 3
Box for base of Three:
- cubes and prisms
- coloured yellow, white, green
small 1cm cubes
prepared tickets for follow-up work
This is a similar presentation to the power of 2. Begin introducing the zero power, as the children are now familiar with it. Put out the three yellow cubes and write a ticket 3 and then flip the ticket and write three to the zero power 30. Can I exchange the blocks? yes, do this
To get to the next power move the three to the right and add two cuboids ( the three yellow cube and a white cuboid). Say,’I have taken three to the zero power three times’ write 3 to the power of 0 x 3, say, I have three to the third power’ flip the ticket and write 31’. Exchange the blocks.
‘I want to taken this to the next power’,Move other the blocks to the right, and add another two, ‘I have taken three to the power of one three times’, Write 31 x3, ‘So what have I now?, I have three to the second power’, flip the ticket and write 32. Exchange the blocks
‘Now I want to go to the next power, so I must taken my three to the second power three times’, add the blocks, ‘What did I do? I took two to the power of three three times’, Write 32 x3, ‘So what did I have? Three to the power of three’, flip the ticket and write 33.
Continue to three to the power of six
Do this as for the base of two, only now the children may have been shown the power of zero at the beginning.
Powers of 10: Reviewing the Wooden Hierarchical Material
2 sets of prepared labels
- 1, 10, 100…1,000,000
- 10 to the powers up to 6 with multiplication on the back:
Say, ‘We have been talking about the powers of numbers, can you lay out the wooden hierarchical material’, then layout the cards saying their names, ‘This is the decimal system and deci means ten, our numbers use the base of ten, so what do we have here? Pick up the card with ‘1’, ‘this is a unit’, turn over the card and change it’s position by ninety degrees, this is ten to the zero power, the unit is the first group and we know the first group has no power, zero power.’
Move to the card with ten. ‘Now we have ten, this is our first group’, turn over the card, ‘we have one unit to the first power, that is a unit to the power one. ’How do we get to the next group?’ (we times by ten), so what have we got?’ Turn the card of 100, ‘I have ten taken ten times, ten to the second power’
Ask the children if they notice anything about the number of zeros.
The children may notice that their are the same amount of zeros as the number in the exponent.
They notice that the geometrical pattern point, line, surface is repeated
To give the child access to keys, emphasising the relationship of the powers to their own number system.
After the lesson:
Play games with the numbers asking which is bigger, e.g. Which would you prefer 102 or 83, 103 or 310, showing the child how to make them
Exponential Notation – Operations
Material for the squares and cubes
‘Today we will do multiplication with the powers using the same base’,
Write the example 33 x32 =
Say, ‘I will take three to the third power, three to the second power number of times. What is three to the second power?’ (9) Indicate the multiplier. (three cubes nine times) Remove a cube and sufficient pieces to form nine cubes in total, ‘I have to build in the powers of three’
‘We went to take our answer in terms of the power of three so we build in the power of three’. Exchange three pieces for a cube (this is the point)
So place three cubes together giving three to the power of four (this is the line)
Place another six cubes, three on either side to show three to the fifth power, making a square. (this is the surface)
Write the answer 35
Write the example 22 x24 =
Say, ‘I will take two to the fourth power, how many is this? Indicate the multiplier. Ask, ‘What does this mean? Two squared taken sixteen times’, the child should recognise two to the power of four as sixteen. Remove a sixteen pieces to form nine cubes, ‘I have to build in the powers of three’
‘We went to take our answer in terms of the power of two so we build in the power of three’. Exchange two pieces to form a cube giving two to the power of three. (this is the point)
Arrange the pieces in two to the fourth power, by placing another set of two cubes by it, making a line of two cubes. And then two to the fifth power by taking taking another two cubes, making a surface. And then two to the sixth power by taking taking another two cubes, forming a point. (following the pattern point like surface)
Write the answer 26
Give more examples till the children make the discovery.
43 x 55 = 54
43 x 40 =43
Build the cubes.
35 ÷ by 32 =
Build the dividend, three to the fifth power, (following the pattern point, line, surface, begin with a cube, three to the third power and then make a line of three, three to the power of a fourth, to make it three to the fifth power make it into a squared surface, so nine cubes)
As we are dividing by the second power we are using squares, so lay each piece out alone counting, ‘one times, two times, three times…twenty seven times, three to the second power is contained is contained within the dividend which is three to the fifth power, which is twenty seven times is three to the power of three’
The answer is twenty-seven to the second power, which can be made into three to the third power.
54 ÷ by 53 =
Build the dividend, five to the fourth power, (following the pattern point, line, surface, take a cube, which is to the third power and then making five cubes in a line)
As we are dividing to the power of a cube we leave the pieces in cubes and separate them, saying, ‘I want to know how many times five to the third power is contained in five to the fourth power (five) and what do we know about five (it is the first power) Lay each cube out alone counting, ‘one times, two times, three times…five times’.
The answer is five to the first power.
Give further examples, e.g. 42 ÷ 42 =40
Help the children to come to the discovery.
If the base is the same all you have to do is subtract the exponent.
Children notice that when the base is the same all you have to do is add the exponents.
We do operations with the same base.
Children can be told that their is a convention in Mathematics that for numbers to the power of zero the exponent does not need to be written, 3 plus 0 is 3.
When to give the lesson:
When the children have worked with the powers of 2,3 and 10
When the children are familiar with the geometrical pattern (point, line, surface)
They can work with the notation of squares and cubes and have worked with multiplication of squares and cubes.
Exponential notation with the decimal system
Pen and paper
‘Today we are going to express decimal system numbers using exponential notation’
‘if I write the number 125 in terms of the categories I have 100+20 +5’. Write this
‘If I took 6, 346 I have 6,000 + 300 + 40 + 6’ Write this
Now I will take the number 200, this time I will write it in terms of exponential notation,
200 = 2 x 100
= 2 x 102
6000 = 6 x 1000
= 6 x103
3 = 3 x 1
3 x 100
30 = 3 x 10
3 x 101
3, 642, ‘What is this really? Let’s decompose it.
3,642 = (3 x 1000) + (6 x 100) +(4 x 10) + (2 + 1)
‘Let’s express it in terms of exponential notation’
3,642 = (3 x 103) + (6 x 102) + (4 x 10) + (2 + 10)
‘There is another way of writing this, we can taken out the multiplication symbol because we know that when you put brackets, you multiply what is outside the bracket by what is inside the bracket.
We can express it like this, the numbers outside the brackets are called the co-efficient’
3,642 = 3(103) + 6(102) + 4 (10) + 2(10)
‘Now we are going to do some addition, we will taken 4,235 and add 1, 509’
4,235 + 1, 509
4, 235 = (4 x 103) + (2 x102) + (3 x10) + (5 x100)
- 1, 509 = (1 x103) + (5 x 102) + (0 x10) + (9 x 100)
5, 744 = (5 x103) + (7 x102) + (3 x 10) + (14 x 100)
‘Beginning with the units,first, expand the addends using exponential notation, then we translate them back into decimal system numbers’
500 + 700 + 30 +14
‘And then we add them’
Check with ordinary addition
216 – 124
216 = (2 x 102) + (1 x 10) + (6 x 100)
- 124 = (1x 102) + (2 x 10) + (4 x 100)
92 = (0 x 102) + (9 x 10) + (2 x 100)
‘It is necessary to exchange, do not show this on paper’
Check with ordinary subtraction
To do this the children must have discovered that to multiply exponential notation with similar bases by adding the exponents.
42 x 3
42 = (4 x 10) + (2 x100)
x 3 (3 x100)
(12 x 10) + (6 x 100)
First multiply the multiplicand, beginning with the units and then add the exponents.
Check using regular multiplication.
4, 239 x 47
4, 239 = (1 x 103) + (2 x 102) + (3 x 10) + (9 x 100)
x 47 = (4 x10) + (7 x 100)
(7 x 103) + (14 x 102) + (12 x 10) + (63 x 100)
(4 x 104) + (8 x 103) + (12 x 102) + (36 x 10)
(4 x 104) + (15 x103) + (26 x 102) + (57 x 10) + (63 x100)
40,000 + 15,000 + 2, 600 + 570 + 63
= 58, 233
First expand the decimal notation into exponential notation, then multiply the co-efficient of the units, tens, hundred and thousands of the multiplicand by the units of the multiplier. Then do the same with the tens of the multiplier.
Then add the multiplications with both the units and tens multiplier. Finally transforms the decimal numbers and add them.
Do this when the children have worked with the materials and have realised that to divide the exponents of numbers with the same base must be subtracted.
6000 ÷ 30
6,000 = 6 x 103 = 2 x 102 = 200
30 3 x 10
First we expand using the powers. Then divide the dividend by the divisor, 6 – 3 is 2, then subtract the exponents, so here the power of three minus the power of 1 makes the power of 2, Finally translate the exponential numbers back to decimal ones.
30,000 = 3 x 104 = 3 x 10 = 30 = 6
5,000 5 x 103 5 5
Firstly, expand the decimal numbers into exponential ones. As you can’t divide the dividend by the divisor, three by five, you multiply what you subtract the exponents, here the power of four minus the power of three, to give the power of one and then work with what you have left (3 x10) and divide that by 5.
75, 000 ÷ 15
75,000 = 75 x 103 5 x 103 = 5,000
15 15 x 100
First expand,divide the dividend by the divisor, 75 by 15 to give 5 and subtract the exponent.
This helps the children to understand the powers of numbers.
It gives a new form of notation and prepares for scientific notation.
These are simple exercises, based on the work in Casa when they used the decimal system cards, with the long multiplication whey are used to analysing the numbers on the bead frame notation paper.
With the keys which have been given with the addition and addicting in what they already know about multiplying and dividing with numbers with the same base, the children can do this work.
- To multiply add exponents with the same base.
- To divide subtract the exponents.