Find the missing number:

15 points ! ~ see if you know the answer to both you!

Which is the equation of an ellipse with directrices at x = ±4 and foci at (2, 0) and (−2, 0)?

You were told that the amount of time lapsed between consecutive trades on the new york stock exchange followed a normal distribution with a mean of 15 seconds. you were also told that the probability that the time lapsed between two consecutive trades to fall between 16 to 17 seconds was 13%. the probability that the time lapsed between two consecutive trades would fall below 13 seconds was 7%. what is the probability that the time lapsed between two consecutive trades will be between 14 and 15 seconds?