If Lea goes grocery shopping every 4th day. How many times a week does she go grocery shopping ?

In a month with 30 days 

and four seven day weeks in it, 

Lea will go shopping once during the first week 

and twice a week during the following three weeks. 

Otherwise, just once.

She only goes once a week.

If Lea goes grocery shopping every 4th day, 

she goes 6 times a week grocery shopping. 

7/4  times in a week.

Gee, I think it might be 2x a week, but different days.