Learn French: J'ai vingt et un collègues dans mon équipe.

In French, numbers ending in 1 from 21 to 71 use et (and) to connect the tens and the ones. So 21 is literally "twenty and one". For other numbers, like 22, you drop the et and just use a hyphen, like vingt-deux.

Do I pronounce the "t" at the end of vingt?

Usually, the "t" at the end of vingt is silent. However, because the next word et starts with a vowel, you pronounce the "t" to smoothly link the words together. You will hear the "t" sound spoken clearly.

Would the un in 21 ever change to une?

Yes! If you are counting something feminine, the 1 changes to match it. For example, 21 cars would be vingt et une voitures. Here, collègues can be either masculine or feminine, so we use the default masculine un for a mixed group.

Why is it mon équipe if équipe is a feminine word?

Normally, you use ma for feminine words. But because équipe starts with a vowel, saying ma équipe would put two vowel sounds right next to each other. To make it flow better when speaking, French uses the masculine mon instead.