The sum of the digits of a two digit number is 7. When the digits are reversed, the number is decreased by 9. Find the number.
Assume the number is ab.
ATQ
a + b = 7 ....(i)
10 a + b - 10b - a = 9
9( a - b) = 9
a - b = 1....(ii)
Equation (i) + Equation (ii)
2a = 8 => a =4
b = 3
Hence the required number is 43.