If Betty had 60 marbles, she gave Stuart 40/100*60=<<60/100*40=24>>24 marbles.

Since the number of marbles in Stuart's collection increased to 80 after Betty gave him 24 marbles, the number of marbles he initially had is 80-24=<<80-24=56>>56

# Answer

56
Question:
After Betty gave Stuart 40% of her marble collection, the number of marbles in Stuart's collection increased to 80. If Betty had 60 marbles, how many marbles did Stuart have initially?
Answer:
Let's think step by step.

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56
After Betty gave Stuart 40% of her marble collection, the number of marbles in Stuart's collection increased to 80. If Betty had 60 marbles, how many marbles did Stuart have initially?
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