Give diferents permision to several groups?

["Eliezer Figueroa" <efigueroa@hotmail.com>]

I have a Folder name folder1 an 2 groups, group1 and group2.
I want group1 to be able to change all the files inside folder1. But at 
the same time I want group2 to only read the files in folder1. I do not 
want to give any permission to any other users.
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