Solution
= Solution
The <Born rule> says that the probability of a projective-measurement outcome is the squared norm of the state projected onto the corresponding eigenspace. The basis vectors in the state whose second qubit is one are
$$
|010\rangle,\qquad |110\rangle,\qquad |111\rangle.
$$
They are mutually orthogonal, so
$$
\boxed{\mathbb P(\text{second qubit}=1)
=|b|^2+|c|^2+|d|^2}.
$$