Question

a number consists of two digits. the digit at the tens place is twice that of the digit at units place. if 18 is subtracted from the number, the digits are reversed. find the number.

Answer 1

let the digit of tens place is x and unit place is y .

the number is 10x + y

according to questions ,
then , x = 2y
so, x-2y = 0-----------------1 equation

now , according to question 18 is subtracted from the number, the digits are reversed

=> 10x+y -18= 10y+x

=> 10x-x +y-10y = 18

=> 9x - 9y = 18

=> x - y = 2 ----------------2. equation

now , subtract 1 equation from 2 equation ,

=> x - y - ( x-2y )= 2 - 0

=> x - y - x + 2y = 2

=> y = 2

and x =2y = 4

then , the number = 10x + y = 10×4+2 = 42 Ans