



 
Hi Leah, The first swing went 10 feet and then the second swing went 80% of 10 feet so that is
The third swing went 80% of the length of the second swing so that is
The fourth swing went 80% of the third swing so that is
Now you should be able to see the pattern. The length of the nth swing is
Hence the sum of the lengths of the first swing, the second swing, the third swing, ... the nth swing is
Can you see how to complete the problem now?  


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