Suppose that we are given a fixed pair $a_1, a_2$ of non-zero irrational algebraic integers in some number field $K$ which are independent over $\mathbb{Q}$. Suppose that $\mathcal{P}$ is a prime ideal in $\mathcal{O}_K$, the ring of integers in $K$. For which $\mathcal{P}$ can we find a rational number $b_1/b_2$ say such that $a_1/a_2 \equiv b_1/b_2 \pmod{\mathcal{P}}$?
A second question: Suppose we have two linear forms with algebraic integral coefficients in some number field $K$, linearly independent over $\mathbb{Q}$,
$$\displaystyle a_1 x_1 + a_2 x_2 + a_3 x_3, \text{ } b_1 x_1 + b_2 x_2 + b_3 x_3. $$
Is there a way to estimate the number of solutions of the following congruence
$$\displaystyle a_1 x_1 + a_2 x_2 + a_3 x_3 \equiv b_1 x_1 + b_2 x_2 + b_3 x_3 \equiv 0 \pmod{\mathcal{P}}$$
for prime ideals $\mathcal{P}$ which can be assumed to be sufficiently large in terms of $a_i$'s and $b_i$'s? For a given $\mathcal{P}$, define $E_\mathcal{P}(X)$ to be the number of solutions of the above congruence in integer triplets $(x_1, x_2, x_3) \in \mathbb{Z}^3$ with $|x_i| \leq X$ for $ i = 1,2,3$. Further, we may assume that the rational prime $p$ below $\mathcal{P}$ satisfies $p > X$. Can we obtain a bound of the form
$$\displaystyle \sum_{\substack{\mathcal{P} \\ p > X}} E_\mathcal{P}(X) = o(X^3)?$$
