Negate the following sentence. The sentence is "Bob visits at least one of his siblings every year." My negation of this sentence is "Bob doesn't visit all of his siblings every year." Is this correct? if not, what would be a correct answer and why? I'm familiar with the sentences that are "mathy" or start with a quantifier. That's why I'm not sure about this one.
 A: 
The sentence is "Bob visits at least one of his siblings every year."

Its negation is $$\text{In some year, Bob visits no sibling}\\\exists y \forall s \;\lnot V(s,y)\tag✔.$$

My negation is "Bob doesn't visit all of his siblings every year." Is this correct?

Your suggested negation is ambiguous and could mean either
$$\text{It is not that Bob visits every sibling every year}\\\lnot \forall y \forall s \;V(y,s)\tag{✗1}$$
or
$$\text{Each year, Bob doesn't visit some sibling}\\\forall y \lnot\forall s \; V(s,y)\tag{✗2},$$ both incorrect.

I'm familiar with the sentences that are "mathy" or start with a quantifier. That's why I'm not sure about this one.

Yes, hanging quantifiers potentially gives rise to scope ambiguities, like in your suggested negation.
A: I disagree with ultralegend; I do not view your response as correct. In math, we like to start with the quantifier, so we would say "Every year, Bob visits at least one sibling."
Hence, the negation of this would be "There exists a year where Bob visited none of his siblings."
The important idea is we actually are negating the "every year" aspect as well, which is where the "there exists" comes from.
