5 workers together can build a road in 20 days. Suppose every worker works at the same rate. If 3 workers work on the road for 10 days before 11 more workers join them, then how long total will it take to build the road?

Kevin and randy muise have a jar containing 78 coins, all of which are either quarters or nickels. the total value of the coins in the jar is $13.90. how many of each type of coin do they have?

What is the axis of symmetry of the function f(x)=-(x+ 9)(x-21)

Set $r$ is a set of rectangles such that (1) only the grid points shown here are used as vertices, (2) all sides are vertical or horizontal and (3) no two rectangles in the set are congruent. if $r$ contains the maximum possible number of rectangles given these conditions, what fraction of the rectangles in set $r$ are squares? express your answer as a common fraction.