If Mary weighs 160 lbs, Jamison weighs 160 lbs + 20 lbs = <<160+20=180>>180 lbs.
If John weighs one-quarter less than what Mary weighs, he weighs 1/4 * 160 lbs = <<1/4*160=40>>40 lbs more.
The total weight of John is 160 lbs + 40 lbs = <<160+40=200>>200 lbs.
The total weight for the three is 200 lbs + 180 lbs + 160 lbs = <<200+180+160=540>>540 lbs.
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