Question

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)
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Answer 1

Answer:

let, units digit be x

and ten's digit be y

therefore number= 10y+x

now, 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 = y

therefore y = 3

substituting y = 3 in equ - 1 we get

X = 2y

=> X= 2(3)

=> X = 6

Hence the required number is

10y+x

= 10(3)+6

= 30+6

= 36