2 Digit Numbers Of Whic Their Sum Is 4.If The Digit Number Is Interchanged Their Difference Is 18.What Is The Digit Number
ab = 10 a + b
a + b = 4 so b = (4-a)
10 b + a - 10 a - b = 18
- 9 a + 9 b = 18
-9 a + 9 (4-a) = 18
-18 a = -18
so
a = 1
then b = 3
and the number is 13