In the expression $5 * 4 * 3 * 2 * 1$, * is chosen from $+$, $-$, $\times$ each at most two times. What is the smallest non-negative value of the expression?

A father said to his son, "n years back I was as old as you are now. My present age is four times your age n years back". If the sum of the present ages of the father and the son is 130 years, what is the difference of their ages?

Let $p, q, r$ and $s$ be distinct positive integers. Let $p, q$ be odd and $r, s$ be even. Consider the following statements :

1. $(p - r) (qs)$ is even.

2. $(q - s) q^2 s$ is even.

3. $(q + r)^2 (p + s)$ is odd.

Which of the statements given above are correct?

If the sum of the two-digit numbers AB and CD is the three-digit number 1CE, where the letters A, B, C, D, E denote distinct digits, then what is the value of A?