Question

5.
Consider a 2-digit number such that the ten's digit
is twice that of the unit's digit. Now, if the digits
are reversed and the reversed digit number is
subtracted from the original number, the result is
always divisible by
(1) 5
(2) 9
(3) 7
(4) All of these
want full explanation​

Answer 1

Answer : 9

let the unit digit be x

so ten's digit = 2x

so the number = 20x + x

20 x + x = 21x

when the digits are reversed,

number = 10x + 2x

10x + 2x = 12x

(20 x + x ) - (10x + 2x )

= 21x - 12x

= 9x

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