Answer :
Explanation :

Let the two digits be x & y From given data in the question, we get x + y = 3(x - y) x + y = 3x - 3y => 2x = 4y x/y = 2/1 For having the 2:1, numbers satisfying are 12, 21, 24, 42, 36, 63, 48, 84 From this 36 is eleminated because it is a perfect square and no others are prime or perfect squares. Hence, there exists 7 such 2-digit numbers => 12, 21, 24, 42, 63, 48, 84.