Assume the box contains 9 balls:
4 red, 2 blue, and 3 yellow. a ball is drawn and its color noted. if the ball is yellow, it is replaced; otherwise, it is not. a second ball is then drawn and its color is noted.
what is the probability that the first ball was yellow, given that the second was red?

What is the solution to the system of the equations? x = y - 3 x + 3y = 13

Which best explains why this triangle is or is not a right triangle?

An automated water dispenser fills packets with one liter of water on average, with a standard deviation of 5 milliliter. the manual says that after a year of operation the dispenser should be tested to see if it needs recalibration. a year later a number of filled packets are set aside and measured separately. it is found that the average packet now contains about 0.995 liters. does the dispenser need calibration? explain your answer.