Afriend of yours, a senior, took the graduate record exam in september and scored in the 99th percentile. infebruary, your friend took the same exam over again. this time your friend scored in the 90th percentile. as aresearch methods student, you told your friend that his/her lowered score was most likely due to: differential selection. compensation rivalry. testing. demoralization. statistical regression

"differential selection"

Step-by-step explanation:

If your friend took the test twice and passed both times with a score above 90% then the minor difference in price is most likely due to "differential selection". The first test had  questions that he had a little more experience in solving, while the second time he was most likely given a couple questions that he wasn't as prepared for as he was the first time. This is most likely the cause for the difference in percentiles.

I hope this answered your question. If you have any more questions feel free to ask away at

3. parallelogram

step-by-step explanation:

we turn each of our sides into direction vectors

ab=b-a=(3 - 7, 1 - 0) = (-4, 1)

bc=c-b=(1,6)

cd=d-c=(4,-1)

da=a-d=(-1,-6)

we see how the opposite sides have negated direction vectors; this is characteristic of a parallelogram.   we have congruent sides ab=cd and bc=da with unequal lengths because 1^2+6^2 is different from (-4)^2+1^2.   so it's not a square or a rhombus.  

we check the dot product of direction vectors of adjacent sides.   we have

ab dot bc = -4(1) + 1(6) = 2

that's not zero so the sides are not perpendicular.   we've ruled out rectangle.

the direction vectors indicate two pairs of congruent parallel sides, so we choose parallelogram over trapezoid.