Solution
= Solution
Take the <complement of an event>: fewer than two successes means zero or one. These <mutually exclusive events> have <probabilities> $(1-y)^5$ and $5y(1-y)^4$. Hence
$$
\boxed{\mathbb P(N_L\geq2)=1-(1-y)^5-5y(1-y)^4}.
$$
= Solution
Take the <complement of an event>: fewer than two successes means zero or one. These <mutually exclusive events> have <probabilities> $(1-y)^5$ and $5y(1-y)^4$. Hence
$$
\boxed{\mathbb P(N_L\geq2)=1-(1-y)^5-5y(1-y)^4}.
$$