Learn Italian: Questo gruppo ha tre ragazzi e quattro ragazze. - This group has three boys and four girls.

No! Most Italian numbers, including tre (three) and quattro (four), never change their endings no matter what they are counting. From 1 to 10, the only exception is the number one, which changes to match the gender of the noun (like un ragazzo or una ragazza).

Why does ragazzi end in -i but ragazze ends in -e?

These are the standard plural endings in Italian. The singular word for boy is ragazzo (ends in -o), which becomes ragazzi (ends in -i) in the plural. The singular word for girl is ragazza (ends in -a), which changes to ragazze (ends in -e) in the plural.

How do I pronounce the word ha in this sentence?

The letter h is always silent in Italian, so ha is pronounced exactly like a simple 'a' sound. The h is only there in writing so you can tell the difference between ha (he/she/it has) and the little word a (to/at).

Why is it questo gruppo instead of questa gruppo?

The word questo (this) has to match the gender of the noun it points to. Because gruppo (group) is a masculine word, we use the masculine form questo. If the noun were feminine, it would change to questa.