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With each stroke, a pump removes 2/5 of the air in a container.    

After 3 strokes, what is the fraction of the original amount of air in the container that is left.    

 

Call "x" the original amount of air in the container.   

 

After the 1st stroke, (2/5) of x has been removed ... 3/5 of x is left.    

 

After the 2nd stroke, (2/5) • (3/5) of x has been removed    

                                 (2/5) • (3/5) = 6/25 removed .... 19/25 of x is left.    

 

After the 3rd stroke, (2/5) • (19/25) of x has been removed    

                                 (2/5) • (19/25) = 38/125 removed ... 87/125 of x is left.    

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