Hello, mairjuanaman!

There are a bag of 7 marbles: 3 red, 4 green.

if u pick 2 marbles, what is the probability of choosing one green and one red (order doesn't matter)?

Isn't it 3/7 x 4/6 ? . . . . . no

You found the probability of getting a Red, then a Green . . ..in that order

And: .

Therefore: .

This is the same answer as: .