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8th Class Mathematics Algebraic Expressions Question Bank Algebra

  • question_answer
    A certain number of two digits is four times the sum of its digits. If 9 be added to the number, the digits are reversed. Find the number.

    A) 15                               

    B) 12

    C) 21                               

    D) 51

    Correct Answer: B

    Solution :

    Let the digits of ten?s place and of unit?s place of the number be x and y respectively, such that the number is \[4{{x}^{2}}-20x+25=0\] According to the question, \[10x+y=(x+y)\times 4\]\[\frac{3}{2}\] \[6x=3y=0\] \[\Rightarrow \]\[\frac{5}{2}\]             ?(1) Further, \[10x+y+9=10y+x\] \[\Rightarrow \]\[2{{(a+b)}^{2}}-9(a+b)-5\]                      ?(2) Solving equation (1) and (2), we get \[a+b+5,2a+2b-1\] Hence, the number\[=10\,(1)+2=12.\]


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