<human>:  Mary uses plastic grocery bags that can hold a maximum of twenty pounds. She buys 4 pounds of green beans, 6 pounds milk, and twice the amount of carrots as green beans. How many more pounds of groceries can Mary fit in that bag?
<bot>: How many pounds of green beans are there? ** First find the total weight of the carrots: 4 pounds * 2 = <<4*2=8>>8 pounds
How many pounds of groceries are there? ** Now add the total weight of each item: 6 pounds + 8 pounds + 4 pounds = <<6+8+4=18>>18 pounds
How many more pounds of groceries can Mary fit in that bag? ** Now subtract the total weight of the groceries from the bag's weight limit: 20 pounds - 18 pounds = <<20-18=2>>2 pounds
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