The amount of certain trace element in blood is known to vary with a standard deviation of 24.1 ppm (parts per million) for male blood donors and 19.5 ppm foe female donors. Random sample of 85 male and 60 female donors yield concentration means of 28 and 33 ppm respectively. What is the likelihood that the population means of concentrations of the element are significant for men and women?

Which of the following is an example of an opposing signal? no examplthates given.   i would say, that traffic lights in a city at major intersections direct the flow of traffic in opposite directions so would be an example.also, stop signs on either side of the same street would be an example. at a train crossing, the light for allowing car traffic in opposite directions or not would be another example.