Problema Solution
If you take a particular two-digit number, reverse its digits to make a second two-digit number, and add these two numbers together, their sum will be 21. What is the original number?
Answer provided by our tutors
let
the original number have the digits x and y then it can be written as 10x + y, where x and y are elements from the set {0, 1, ...,9} and y<>0
then the reverse number is 10y + x
the sum of these two numbers together is 21
10x + y + 10y + x = 21
11(x + y) = 21
x + y = 21/11
since x and y are integers their sum is also and integer follows the above equation has no solution thus the there are no such numbers as described in the question.