To make clear, d1 and d0 are two digits (0 <= d1, d0 <= 9). Otherwise, it may seem that n ends with four decimal digits: d, 1, d, 0.

Well, using this hint, suppose 4 | (10 * d1 + d0). Obviously, 4 | 100. Does it imply that 4 | n?It gave me a hint that if the decimal representation of a nonnegative integer n ends in d1d0, then there is an integer s such that n = 100s + 10d1 + d0

Any implication of the form "If A, then B or A" is automatically true.For all integers a and b, if a|b then a|10 or a|b.

There is a couple of LaTeX tutorials in the LaTeX forum.One more thing, where or how can I make a source code out of my problems so they will be easier to read?