Asurvey of a group of seventh graders and a group of teachers at a local middle school asked how many siblings they each have. the dot plots below show the results. students a dot plot titled students. a number line going from 0 to 9 labeled number of siblings. there are 2 dots above 0, 4 above 1, 7 above 2, 5 above 3, 2 above 4, and 0 above 5, 6, 7, 8, and 9. teachers a dot plot titled teachers. a number line going from 0 to 9 labeled number of siblings. there is 1 dot above 0, 3 dots above 1, 2 above 2, 4 above 3, 5 above 4, 3 above 5, 1 above 6, 0 above 7, 1 above 8, and 0 above 9. what is closest to the difference between the means of the two dot plots? 0.5 1.0 1.5 2.0

The correct answer is:

1.5

Explanation:

Attached to this answer is the diagram of the box plot described in the question, and the means from the plot are calculated thus;

Students;    no. of siblings

student 0     2

student 1      4

student 2     7

student 3     5

student 4     2

Total             20

Mean no. of siblings = (total number of siblings) ÷ (total number of students)

Note that number of students here are the once that had at least one sibling, others without siblings are not used in the calculation, hence 5 students (student-0 to student-4) make up total number of students, while the remaining 4 students (student-4 to student-9) are disregarded.

Therefore, mean = 20 ÷ 5 = 4 siblings.

Teachers       No. of Siblings

student 0         1

student 1          3

student 2         2

student 3         4

student 4         5

student 5         3

student 6         1

student 8         1

Total                20

mean = (total number of siblings) ÷ (total number of students)

note that 8 students are used for the calculation, same reason as explained above

mean = 20 ÷ 8 = 2.5

Mean difference between the two plots = 4 - 2.5 = 1.5.

speed

explanation:

the earth’s crust is broken into separate pieces called tectonic plates (fig. 7.14). recall that the crust is the solid, rocky, outer shell of the planet. it is composed of two distinctly different types of material: the less-dense continental crust and the more-dense oceanic crust. both types of crust rest atop solid, upper mantle material. the upper mantle, in turn, floats on a denser layer of lower mantle that is much like thick molten tar.

each tectonic plate is free-floating and can move independently. earthquakes and volcanoes are the direct result of the movement of tectonic plates at fault lines. the term fault is used to describe the boundary between tectonic plates. most of the earthquakes and volcanoes around the pacific ocean basin—a pattern known as the “ring of fire”—are due to the movement of tectonic plates in this region. other observable results of short-term plate movement include the gradual widening of the great rift lakes in eastern africa and the rising of the himalayan mountain range. the motion of plates can be described in four general patterns:

collision: when two continental plates are shoved together

subduction: when one plate plunges beneath another (fig. 7.15)

spreading: when two plates are pushed apart (fig. 7.15)

transform faulting: when two plates slide past each other (fig. 7.15)