Well if 1/5 of the groceries are produce and 2/3 of the produce is veggies... then to find how much of the total groceries are veggies we have to find 2/3 of 1/5.
In math
"of" means ×
"is" means =
2/3 of 1/5 is
2/3 × 1/5 = 2/15
2/15 of the groceries are veggies