The sum of the digits of my age is equal to one
more than the product of the digits.
t = the tens digit of my age
u = the ones or units digit of my age
t+u = tu+1
t-tu = 1-u
t(1-u)=1-u
t=(1-u)/(1-u)
t=1
So the tens digit is 1.
This year, my age is a multiple of 4.
So my age is either 12 or 16, since those are the only
two-digit multiples of 4 with tens digit 1.
Three years ago, my age was a prime number.
I can't be 12, for if I were, three years ago I would have been 9,
but 9 is not a prime number. So I must be 16, for 3 years ago I
was 13, which is a prime number.
So my age is 16.
I have a brother whose age twenty years ago was
half my current age.
Half my age is 8, so for my brother to have been 8 years old 20
years ago, he must now be 8+20 or 28.
Edwin