Multiple Choice Questions on In a two digit number the digit at the unit rsquo s place is 1 less than twice the digit at nbs........... for Mathematics - All Exams Preparation

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Multiple Choice Questions

In a two digit number the digit at the unit rsquo s place is 1 less than twice the digit at nbs...........

Quantitative Aptitude ( CCS) Number System
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    In a two-digit number, the digit at the unit’s place is 1 less than twice the digit at the ten’s place. If the digits at unit’s and ten’s place are interchanged, the difference between the new and the original number is less than the original number by 20. The original number is

    23

    Incorrect Answer

    35

    Incorrect Answer

    47

    Correct Answer

    59

    Incorrect Answer
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    Explanation:

    Let unit’s digit be x and ten’s digit by y
    ∴ Number formed = 10y + x …(i)
    According to the question,

    2y – 1 = x …(ii) 
    Also, (New number) – (Original number) 
    = Original number – 20 
    (10x + y) – (10y + x) = (10y + x) – 20 
    10x + y – 10y – x = 10y + x – 20 
    9x – 9y = 10y + x – 20 …(iii) 
    On substituting the value of x = 2y – 1 from equation (i), we get 
    9 (2y – 1) – 9y = 10y + 2y – 1 – 20
    ⇒ 18y – 9 – 9y = 10y + 2y – 1 – 20 
    ⇒ 3y = 12 
    ∴ y = 4 
    On putting the value of y in equation (ii), we get 
    x = 2 × 4 – 1 
    = 8 – 1 = 7 
    ∴ Required number
    = 10y + x
    = 10 × 4 + 7 = 47 

    By: Amit Kumar
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