Quantative aptitude problems

Q1.the sum of a digit of a two digit number is 10.If 18 is subtracted from it the digits in the resulting number will be equal.the number is .........?
 

Please teach me how to solve this....

thanks

let two digits are X & Y

AS PER QUESTION,

X + Y = 10 ---------------------------(1)

X - 18 = Y

OR, X -Y = 18 -----------------------(2)

AFTER SOLVING THIS EQUATION,

U GET, X = 14 & Y = -4.

http://www.caclubindia.com/forum/cpt-maths-question-200005.asp

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Let x = 10's digit of a two digit number
Let y = units digit
Let z = the resulting equal digits
:
Write an equation for each statement:
:
"the sum of a two digit number is 10."
x + y = 10
or
y = (10-x)
:
" if 18 be subtracted from it, the digits in the resulting number will be equal."
10x + y - 18 = 10z + z
10x + y = 11z + 18
:
Substitute (10-x) for y
10x + (10-x) = 11z + 18
10x - x = 11z + 18 - 10
9x = 11z + 8
:
The single digit integer values for x and z are limited to x=7 and z=5 in this equation:
x = 7, y = 3, z = 5
:
The number is 73
:
Check in the statement:
"if 18 be subtracted from it, the digits in the resulting number will be equal."
73 - 18 = 55