NUMBERS
We know that when we count we start 1,2 …. . But there are other numbers like 0, negative numbers and decimals.
All these types of numbers are categorized in different groups like counting numbers, integers, real numbers, whole numbers and rational and irrational numbers according to their properties. all this have been covered in this chapter
Base Ten Numeration
Numbers are represented by symbols called numerals. For example, numeral for the number ten is 10. Numeral for the number hundred is 110 and so on.
The symbols which represent numbers are called digits. For example the number 521 has three (3) digits which are 5, 2 and 1. There are only tendigits which are used to represent any number. These digits are 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.
The Place Value in each Digit in Base Ten Numeration
Identify the place value in each digit in base ten numeration
When we write a number, for example 521, each digit has a different value called place value. The 1 on the right means 1 ones which can be written as 1 × 1, the next number which is 2 means 2 tens which can be written as 2 × 10 and the last number which is 5 means 5 hundreds which can be written as 5 × 100. Therefore the number 521 was found by adding the numbers 5 × 100 + 2 × 10 + 1× 1 = 521.
Note that when writing numbers in words, if there is zero between numbers we use word ‘and’
Example 1
Write the following numbers in words:
- 7 008
- 99 827 213
- 59 000
Solution
- 7 008 = Seven thousand and eight.
- 99 827 213 = Ninety nine millions eight hundred twenty seven thousand two hundred thirteen.
- 59 000 = Fifty nine thousand.
Example 2
Write the numbers bellow in expanded form.
- 732.
- 1 205.
Solution
- 732 = 7 x 100 + 3 x 10 + 2 x 1
- 1 205 = 1 x 1000 + 2 x 100 + 0 x 10 + 5 x 1
Example 3
Write in numerals for each of the following:
- 9 x 100 + 8 x 10 + 0 x 1
- Nine hundred fifty five thousand and five.
Solution
- 9 x 100 + 8 x 10 + 0 x 1 = 980
- Nine hundred fifty five thousand and five = 955 005.
Example 4
For each of the following numbers write the place value of the digit in brackets.
- 89 705 361 (8)
- 57 341 (7)
Solution
- 8 is in the place value of ten millions.
- 7 is in the place value of thousands.
Numbers in Base Ten Numeration
Read numbers in base ten numeration
Base Ten Numeration is a system of writing numbers using ten symbols i.e. 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9. Base Ten Numeration is also called decimal system of Numeration.
Numbers in Base Ten Numeration up to One Billion
Write numbers in base ten numeration up to one billion
Consider the table below showing place values of numbers up to one Billion.
Billions |
Hundred millions |
Ten millions |
Millions |
Hundred Thousands |
Ten Thousands |
Thousands |
Hundreds |
Tens |
Ones |
1 | |||||||||
1 | |||||||||
1 | |||||||||
1 | |||||||||
1 | |||||||||
1 | |||||||||
1 | |||||||||
1 | |||||||||
1 | |||||||||
1 |
If you are given numerals for a number having more than three digits, you have to write it by grouping the digits into groups of three digits from right. For example 7892939 is written as 7 892 939.
When we are writing numbers in words we consider their place values. For example; if we are told to write 725 in words, we first need to know the place value of each digit. Starting from right side 5 is in the place value of ones, 2 is in the place value of tens and seven is in the place value of hundreds. Therefore our numeral will be read as seven hundred twenty five.
Numbers in Daily Life
Apply numbers in daily life
Numbers play an important role in our lives. Almost all the things we do involve numbers and Mathematics. Whether we like it or not, our life revolves in numbers since the day we were born. There are numerous numbers directly or indirectly connected to our lives.
The following are some uses of numbers in our daily life:
> Calling a member of a family or a friend using mobile phone.
> Calculating your daily budget for your food, transportation, and other expenses.
> Cooking, or anything that involves the idea of proportion and percentage.
> Weighing fruits, vegetables, meat, chicken, and others in market.
> Using elevators to go places or floors in the building.
> Looking at the price of discounted items in a shopping mall.
> Looking for the number of people who liked your post on Facebook.
> Switching the channels of your favorite TV shows.
> Telling time you spent on work or school.
> Computing the interest you gained on your business.
Operations with Whole Numbers
We have four operations which are: addition (+), subtraction (-), multiplication ( X) and division (÷).
Addition of Whole Numbers
Add whole numbers
When adding numbers we add the corresponding digits in their corresponding place values and we start adding from the right side i.e. from the place value of ones to the next.
We can add numbers horizontally or vertically.
Horizontal addition
Example 5
- 972 + 18=
- 23 750 + 250 =
Solution
- 972 + 18 = 990
- 23 750 + 250 = 24 000
Example 6
Subtraction of Whole Numbers
Subtract whole numbers
Subtraction is denoted by the sign (-). It is sometimes called minus. Subtraction is the opposite of addition. Subtraction also means reduce a number from certain number and the answer that is obtained is called difference..
Subtraction is done in similar way like addition. We subtract the corresponding digits in their corresponding place value. For example; 505 – 13.
We first subtract ones, which are 5 and 3. Subtract3 from 5 gives 2. Followed by tens which are 0 and 1.
Subtract 1 from 0 is not possible. In order to make it easy, take 1 from 5 (hundreds). When 1 is added to 0 it has to be changed to be tens since it is added to a place of tens.
So, when 1 comes into a place of tens it becomes 10. So add 10 to 0. We get 10. Now, subtract 1 from 10. We get 9. We are left with 4 in a place of hundreds since we took 1. There for our answer will be 492.
Note that similar manner will be used when subtracting.
Example 7
Multiplication of Whole Numbers
Multiply whole numbers
Multiplication means adding repeatedly depending on the times number given. For example; 25 6 means add 25, repeat adding 6 times i.e. 25 + 25 + 25 + 25 +25 + 25 = 150. The answer obtained after multiplying two or more numbers is called product.
The number being multiplied is called a multiplicand while the number used in multiplying is called a multiplier. Referring our example, 25 is multiplicand and 6 is multiplier.
Example 8
Division of Whole Numbers
Divide whole numbers
Division is the same as subtraction. You subtractdivisor(the number used to divide another number) from dividend (the number which is to be divided), we repeat subtracting divisor to the answer obtained until we get zero. The answer is how many times you repeat subtraction.
For example; 27 ÷9, we take 27 we subtract 9, we get 18. Again we take 18 we subtract 9, we get 9. We take 9 we subtract 9 we get 0. We repeat subtraction three times. Therefore the answer is 3.
The answer obtained is called quotient.
Referring to our example; 27 is dividend, 9 is divisor and 3 is quotient. If a number can’t be divided exactly, what remains or left over is calledremainder.
Example 9
The Four Operations in Solving Word Problems
Use the four operations in solving word problems
Sometimes you may be given a question with mixed operations +, -, xand ÷ . We do multiplication and division first then addition and subtraction.
Example 10
- 12 ÷ 4 + 3 x 5
- 14 x2 ÷ 7 – 3 + 6
Solution
- 12 x 4 + 3 x 5 =3 + 15 (do division and multiplication fist) =18
- 14 x 2 ÷ 7 – 3 + 6 =28 ÷ 7 – 3 + 6 (multiply first) =4 – 3 + 6 (then divide) =10 – 3 (add then subtract) =7
We may use brackets to separate x,÷ , + and – if they are mixed in the same problem and use what is called BODMAS . BODMAS is the short form of the following:
B for Brackets O for Open D for Division M for Multiplication A for Addition and S for Subtraction
Therefore, with mixed operations, we first do the operation inside the brackets; we say that we open the brackets. Then we do division followed by multiplication, addition and lastly subtraction.
Example 11
There are 30 Tomatoes in each row
4 rows will have 30 × 4 = 120 Tomatoes
6 rows have 25 × 6 = 150 Cabbages
Each row has 15 Water Lemons
3 rows have 15 × 3 = 45 Water Lemons
In total there 120 + 150 + 45 = 315 plants.
Therefore in Juma’s mother garden there are 315 plants.
Example 14
A school shop collects sh 90 000 from customers each day. If sh 380 000 from the collection of 6 days was used to buy books. How much money was left?
Each day the collection is sh 90 000
6 days collection is sh 90 000 × 6 = sh 540 000
The money left will be = Total collection – Money used
= sh 540 000 – sh 380 000 = sh 160 000
Therefore the money left was sh 160 000
Exercise 1
1. For each of the following numbers write the place value of a digit in a bracket.
- 899 482 (4)
- 1 940 (0)
- 9 123 476
2. Write the numerals for each of the following problems.
i. Ten thousand and fifty one.
ii. Nine hundred thirty millio
Factors of a Number
Find factors of a number
Consider two numbers 5 and 6, when we multiply these numbers i.e. 5 6 the answer is 30. The numbers 5 and 6 are called factors or divisors of 30 and number 30 is called a multiple of 5 and 6. Therefore factors are the divisors of a number.
Example 15
Find all factors of 12
Note that, when listing the factors we don’t repeat any of it.
Consider a number line below
The numbers from 0 to the right are called positive numbers and the numbers from 0 to the left with minus (-) sign are called negative numbers. Therefore all numbers with positive (+) or negative (-) sign are called integers and they are denoted by Î–. Numbers with positive sign are written without showing the positive sign.
For example +1, +2, +3, … they are written simply as 1, 2, 3, … . But negative numbers must carry negative sign (-). Therefore integers are all positive and negative numbers including zero (0). Zero is neither positive nor negative number. It is neutral.
The numbers from zero to the right increases their values as the increase. While the numbers from zero to the left decrease their values as they increase. Consider a number line below.
If you take the numbers 2 and 3, 3 is to the right of 2, so 3 is greater than 2. We use the symbol ‘>’ to show that the number is greater than i. e. 3 >2(three is greater than two). And since 2 is to the left of 3, we say that 2 is smaller than 3 i.e. 2<3. The symbol ‘<’ is use to show that the number is less than.
Consider numbers to the left of 0. For example if you take -5 and -3. -5 is to the left of -3, therefore -5 is smaller than -3. -3 is to the right of -5, therefore -3 is greater than -5.
Generally, the number which is to the right of the other number is greater than the number which is to the left of it.
If two numbers are not equal to each to each other, we use the symbol ‘≠’ to show that the two numbers are not equal. The not equal to ‘≠’ is the opposite of is equal to ‘=’.
Example 21
Represent the following integers Î– on a number line
- 0 is greater than Î– and Î– is greater than -4
- -2 is less than Î– and Î– is less than or equal to 1.
a. 0 is greater than Î– means the integers to the left of zero and Î– is greater than -4 means integers to the left of -4. These numbers are -1, -2 and -3. Consider number line below
b. -2 is less than Î– means integers to the right of -2 and Î– is less than or equal to 1 means integers to the left of 1 including 1. These integers are -1, 0 and 1. Consider the number line below
Example 22
Put the signs ‘is greater than’ (>), ‘is less than’ (<), ‘is equal to’ (=) to make a true statement.
Addition of Integers
Show a picture of 2 and 3 on a number line.
When drawing integers on a number line, the arrows for the positive numbers goes to the right while the arrows for the negative numbers goes to the left. Consider an illustration bellow.
The distance from 0 to 3 is the same as the distance from 0 to -3, only the directions of their arrows differ. The arrow for positive 3 goes to the right while the arrow for the negative 3 goes to the left.
Example 24
Solution
Subtraction of Integers
Since subtraction is the opposite of addition, if for example you are given 5-4 is the same as 5 + (-4). So if we have to subtract 4 from 5 we can use a number line in the same way as we did in addition. Therefore 5-4 on a number line will be:
Take five steps from 0 to the right and then four steps to the left from 5. The result is 1.
Multiplication of Integers
Example 25
2×6 is the same as add 2 six times i.e. 2×6 = 2 + 2 + 2 + 2 + 2 +2 = 12. On a number line will be:
Multiplication of a negative integer by a negative integer cannot be shown on a number line but the product of these two negative integers is a positive integer.
From the above examples we note that multiplication of two positive integers is a positive integer. And multiplication of a positive integer by a negative integer is a negative integer. In summary:
- (+)×,(+) = (+)
- (-)×,(-) = (+)
- (+)×,(-) = (-)
- (-)×,(+) = (-)
Division of Integers
Example 26
6÷3 is the same as saying that, which number when you multiply it by 3 you will get 6, that number is 2, so, 6÷3 = 2.
Therefore division is the opposite of multiplication. From our example 2×3 = 6 and 6÷3 = 2. Thus multiplication and division are opposite to each other.
Dividing two integers which are both positive the quotient (answer) is a positive integer. If they are both negative also the quotient is positive. If one of the integer is positive and the other is negative then the quotient is negative. In summary:
- (+)÷(+) = (+)
- (-)÷(-) = (+)
- (+)÷(-) = (-)
- (-)÷(+) = (-)
Mixed Operations on Integers
Perform mixed operations on integers
You may be given more than one operation on the same problem. Do multiplication and division first and then the rest of the signs. If there are brackets, we first open the brackets and then we do division followed by multiplication, addition and lastly subtraction. In short we call it BODMAS. The same as the one we did on operations on whole numbers.
Example 27
=3 + 6 -1 (first divide and multiply)
=8 (add and then subtract)
Example 28
=1 + 4 – 7 (do operations inside the brackets and divide first)
umbers are represented by symbols called numerals. For example, numeral for the number ten is 10. Numeral for the number hundred is 110 and so on.
- READ TOPIC 2: Fractions
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