One share of a stock costs $80 one day and $75 the next. What is the percent decrease? Enter the number only. Do not enter the % sign. Please help this out.

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White shapes and black shapes are used in a game. some of the shapes are circles. while the rest are squares. the ratio of the number of white shapes to the number of black shapes is 5: 11. the ratio of the number of white cicrles to the number of white squares is 3: 7. the ratio of the number of black circles to the number of black squres is 3: 8. work out what fraction of all the shapes are circles.