In trapezoid $abcd$, the parallel sides $ab$ and $cd$ have lengths of 8 and 20 units, respectively, and the altitude is 12 units. points $e$ and $f$ are the midpoints of sides $ad$ and $bc$, respectively. what is the area of quadrilateral $efcd$ in square units?

Look at arnold's attempt to solve the equation for b: 3b = 12 b = 3 · 12 b = 36 describe the mistake that arnold made.

Suppose that 3% of all athletes are using the endurance-enhancing hormone epo (you should be able to simply compute the percentage of all athletes that are not using epo). for our purposes, a “positive” test result is one that indicates presence of epo in an athlete’s bloodstream. the probability of a positive result, given the presence of epo is .99. the probability of a negative result, when epo is not present, is .90. what is the probability that a randomly selected athlete tests positive for epo? 0.0297

The triangles are similar. what is the value of x? enter your answer in the box.