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7. In a 2-digit number, digit in units place is twice the digit in tens place. If 27 is added to it, digits are reversed. Find the number.(NCERT Exemplar)​

Answer»

let, UNITS digit be x and ten's digit be ytherefore number= 10y+xnow, according to question,we have X=2y-- [ 1 ]also, 10y+x+27 = 10x+y=> 9y+27 = 9x=> 9y+27 = 9(2y) [ since x=2y ]=> 9y+27 = 18y=> 27 = 18y - 9y=> 27 = 9y=> 27/9 = y=> 3 = ytherefore y = 3substituting y = 3 in EQU - 1 we get X = 2y=> X= 2(3)=> X = 6Hence the required number is 10y+x= 10(3)+6= 30+6= 36


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