Question

The sum of the digits of a two-digit number is 5. If nine is subtracted from the number, the digits will be reversed. Find the Algebraic equation by replacing the tens digit with x.

Answer 1

Let a be the number in the 10s place and b in the 1s place. Then the original two-digit number is 10a + b.

The sum of the digits is 5:

a + b = 5

Subtract 9 from the original number, and we get the same number with its digits reversed:

(10a + b) - 9 = 10b + a

Simplifying this equation gives

9a - 9b = 9

or

a - b = 1

Add this to the first equation above:

(a + b) + (a - b) = 5 + 1

2a = 6

a = 3

Then

3 - b = 1

b = 2

So the original number is 32. Just to check, we have 3 + 2 = 5, and 32 - 9 = 23.