First find the total difference in weight between the two people: 60 pounds - 40 pounds = <<60-40=20>>20 pounds

Then divide the weight difference by the weight of each rock to find the number of rocks need to even the weights: 20 pounds / 4 pound/rock = <<20/4=5>>5 rocks

# Answer

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<|im_start|>system
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<|im_start|>user
Jack, who weighs 60 pounds, wants to play on the see-saw with his cousin Anna, who weighs 40 pounds. How many 4-pound rocks does Jack need to hold to make their weights equal?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
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user
5
Jack, who weighs 60 pounds, wants to play on the see-saw with his cousin Anna, who weighs 40 pounds. How many 4-pound rocks does Jack need to hold to make their weights equal?
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