probability of over-cards

[Paul Thomson]

Hi Guys -

Sorry for the elementary question, I'm bad at probability.

What is the probability of over-cards landing on the flop in hold'em.

For example, if the Hero holds 88.

What is the probability of one over card on the flop? two over cards? and 3 over-card?

More advanced...what if the Villain holds A2? of AJ?

Thx in advance. I can probably figure out how to calculate in the future if u show the math.