Assume the number is abc.
ATQ
a + b + c =10 ...(i)
b = a+c..(ii)
Put value of (a+c) in equation (i)
b +b =10
b = 5 = a+c ...(iii)
100 c + 10b + a - 100a - 10b - c = 99
99(c-a) = 99
c - a = 1 ...(iv)
Equation (iii) + Equation (iv)
a + c + c - a = 1+5
2c = 6
c = 3
a = 2
Hence the required number is 253.