SOLUTION: In a two digit number , the digit at unit's place is equal to the square of the digit at tens place . If 54 is added to the number , the digit gets interchanged . Find the number.

Question 695143: In a two digit number , the digit at unit's place is equal to the square of the digit at tens place . If 54 is added to the number , the digit gets interchanged . Find the number.
Answer by pmatei(79) (Show Source): You can put this solution on YOUR website!
First you need to know how you can write a number of two digits:
23=2*10+3
Following the example above, now my number is xy
xy=x*10+y
and the reverse digits number is yx
yx=y*10+x
What we know is:

and

Bring everything to the right side in the second equation:

Divide entire equation by 9:

Replace y with

So x is either 3 or -2. The second choice cannot be as a digit in a number cannot be negative. So and . Thus the number is 39.
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