Real numbers for class 10 board 2020-2021


we have already studied about the natural number, whole number, integers, and real number as well in class 9. Now in class 10th, we will study more about the real numbers. we will study Euclid’s division lemma, Euclid’s division algorithm, and the fundamental theorem of arithmetic in real numbers for class 10. Before learning real numbers for class 10, let’s recall the real number of class 9. If you would like to practice the standard problem to strengthen your learning concept, you can further check the important Question of the real numbers for class10

Definition and types of real numbers

Real number -: Real number are those numbers which can be represented on the number line


The numbers which we use in real life are called the  Real number.

The real numbers are of two types

  •       Rational number
  •       Irrational number

Rational number -: Those numbers which can be expressed in the form of p/q where p and q are integers and q≠0 is called a rational number.

example – 2\5, 1 , 2.5 …………….etc

Irrational number -: Those numbers which cannot be expressed in the form of p/q is called Irrational number

example-√2, √5, √7 ……..etc

                 some important terms definition for Real number

Prime number-: The number is said to be a prime number if it is exactly divisible by 1 and itself only.

Example – 2, 3, 5 ………..etc.

Composite number-: The number which has more than 2-factor or2 prime factor is called a composite number

Example- 4,6,8,10  ……………etc.

Coprime number -: Two numbers are said to be coprime if their HCF is 1.

Example – 3 and 5 are coprime because their HCF is 1.

Terminating decimal number -: The rational number in which value gets terminate after fixed decimals place is called Terminating decimal number.

Example -25/100  on the division will terminate after 2 decimal places

Non-terminating decimal number -: The number which values do not terminate after the decimal point is called non-terminating decimal number.

Example -3.1415……, 0.3333…., etc

      There are two types of non-terminating decimal representation 

  1.  Pure recurring decimals
  2.  Mixed recurring decimals

Pure recurring decimals -:   A decimal in which all the digits after the decimal point are repeated is called pure recurring decimals.

Example – 0.33…., 1.515151……. etc

mixed recurring decimals -: A decimal in which at least one of digits after the decimal point is not repeated and then some digits or digits repeated is called mixed recurring decimals

Example-2.1666….,0.35555…., 0.78585….. etc

                                                    Important points for  real number

  • All the terminating and recurring decimal are rational number 
  • Non-terminating decimals are  irrational number
  • 2 is only even prime number 
  • 4 is the smallest composite number 

                                  Real numbers for class 10

Lemma -: A lemma is a proven statement that is used to prove other statements.

Algorithm-: An algorithm means a series of well-defined steps that provide a procedure of calculations repeated successively on the results of earlier steps until the desired result is obtained.

                                                     Euclid’s division  lemma

It is nothing but a statement of the long division.consider a division of two positive integers 45 and 8 .when you ask for division, what you will do?

You will think about the number which is multiple of 8 but does not exceed 45 so that our remainder should always less than 8.

when we divide it we will get the result of two more positive integers, namely 5  which is Quotient and 3 which is the remainder.   so our results can be express as

                                                                              43= 8* 5 +5 

This is nothing but Euclid’s division lemma

Euclid’s division lemma -: Let a and b any positive integers then, there exist unique integers q and r such that a=bq+r where 0≤r≤b

Euclid’s division algorithm-: It is an algorithm (procedure) to compute the highest common factor (HCF) of two positive integers, using Euclid’s division lemma. let’s understand it with an example

Q.1 Use Euclid’s division algorithm to find HCF of 210 and 55.

sol. we have two positive integers 210 and 55, applying Euclid’s division lemma, we get

210= 55 * 3 + 45

since the remainder is not 0. so we will apply same things for 55 and 45, then we get

55= 45 *1 + 10

again the remainder is not o, so we continue the same process until the remainder becomes 0.

45= 10 *4 + 5

10= 5*2 + 0

Here remainder is 0, so HCF of 210 and 55 will be 5

                                          Fundamental theorem of arithmetic 

Every composite number can be expressed as the product of prime factor and this factorization is unique except for the order in which the prime factor occurs.

Ex – we have already studied about the composite number and prime number above.

we know, 4 is the smallest composite number, we can express  it as the product of prime numbers

4=  2* 2

similarly, we can express every composite number as prime factors

                                                               HCF and LCM

LCM(Least common multiple ) -: LCM  of two or more numbers is the least number which is divisible by given number completely.

Ex – 16 and 32, the least number which is divisible by 16 and 32 is 32

HCF(Highest common factor)=HCF of two or more number is the largest number which divides the given number completely

The  largest number which divides the given number  16 and 32   completely  is 16


Leave a Comment