<human>:  If Mark weighs 150 pounds and Susan weighs 20 pounds less than Mark. And their friend Bob weighs twice as much as Susan. What is the average weight of the 3 friends?
<bot>: How much does Susan weigh? ** Susan weighs 150 pounds - 20 pounds = <<150-20=130>>130 pounds.
How much does Bob weigh? ** Bob weighs 2 * 130 pounds = <<2*130=260>>260 pounds.
What is the total weight of the 3 friends? ** The friends total weight is 150 + 130 + 260 pounds = <<150+130+260=540>>540 pounds.
What is the average weight of the 3 friends? ** The friends' average weight is 540 pounds / 3 = <<540/3=180>>180 pounds.
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