Let’s take an Example

54 is a 2 digit number.

 

Digits at ten places = 5

Digit at units place = 4

 

So, the number will be

Number = (10 × Digits at ten place) + (1 × Digit at units place)

        = (10 ×  5) + (1 ×  4)

        = 50 + 4

        = 54

 

To generalize

Number

Digits are interchanged

Let number be

    ab

 

So, Digit at tens place = a

  & Digit at unit place = b

 

Number

  = (10 × Digit at tens place)  
      +  (1 × Digit at units place)

     = (10 × a) + (1 × b)

= 10a + b

Thus, number will be

    ba

 

So, Digit at tens place = b

  & Digit at unit place = a

 

Number

  = (10 × Digit at tens place)  
      +  (1 × Digit at units place)

     = (10 × b) + (1 × a)

= 10b + a

  1. Chapter 2 Class 8 Linear Equations in One Variable
  2. Concept wise

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Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.