Question

A number consist of two digits whose sum is 9 If 9 is subtracted from the number its digit are interchanged find the numbers

Answer 1

hye'

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let the number be xy

digit at tens place = 10x

ones place = y

sum is 9

=>x +y = 9

=> x  = 9 -y  .........[1]

f 9 is subtracted from the number its digit are interchanged 

=>(10x +y) - 9 = 10y +x.............[2]

=>now lets put [1] in [2]

=>since  >(10x +y) - 9 = 10y +x and x  = 9 -y 

=>10(9-y) + y -9 = 10y +9-y

=>90 - 10y +y - 9 = 9y +9

=>81 - 9y = 9y +9

=>81 - 9 = 9y +9y

=>72 - 18y

=>y = 4

since x is 9 -y

=> 9 -4

=>5

=>so the original number is 54

hope it helps u.....