PREP里的3道DS题

Q1:

What is the average (arithmetic mean) height of the n people in a certain group?

(1)   The average height of the
       3/n tallest people in the group is 6 feet 5n/2 inches, and the average height of the rest of people in the group is 5 feet 10 inches.

(2)   The sum of the heights of the n people is 178 feet 9 inches.

答案是A

(2)不充分吗?我觉得(2)比(1)还直接呢，后面的数除以n不就好了？

Q2:

Is the measure of  one of the interior angles of quadrilateral ABCD  equal to 60 degrees?

(1) Two of the interior angles of  ABCD are right angles.

(2) The degree measure of angle ABC is twice the degree measure of angle BCD.

答案是E

Q3:

我怎么觉得是c啊？！

problem 1: if n is unknown, 3/n in your expression means number not portion,

then n can only be 3 (not 1) considering the second condition.

there you go.

Problem 2 is E. multiple cases

Problem 3 is E. multiple cases