Harvest time

Grandma and granddaughter Julka reap currants in 15 hours of working together. Julka herself would have currants 10 days after 6 hours of work a day.
Find by what percentage the grandma's harvest time was shortened when the granddaughter was involved in current harvesting.

Result

p =  25 %

Solution:

j=10 6=60 h  15/b+15/j=1 15/b+15/60=1 15/b=115/60=34=0.75 b=15115/60=20 h  p=100 b15b=100 201520=25=25%j = 10 \cdot \ 6 = 60 \ h \ \\ \ \\ 15/b + 15/j = 1 \ \\ 15/b + 15/60 = 1 \ \\ 15/b = 1 - 15/60 = \dfrac{ 3 }{ 4 } = 0.75 \ \\ b = \dfrac{ 15 }{ 1 - 15/60 } = 20 \ h \ \\ \ \\ p = 100 \cdot \ \dfrac{ b-15 }{ b } = 100 \cdot \ \dfrac{ 20-15 }{ 20 } = 25 = 25 \%



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