[讨论]XDF DS-Sec3-Q3, 8

XDF Math, DS, Section 3

Q3: What was Bill's average grade for all of his courses?

(1) His grade in social studies was 75, and in science was 75

(2) His grade in math was 95

I can see that neither (1) nor (2) alone is sufficient. So it's either C or E. The anwer given is E. My question is, can I assume Bill is not taking anything besides Social Studies, Science and Math? If so, then C would be correct.

Q8. Claire paid a total of $1.6 for stamps, some of which cost $0.20 each, and the rest of which cost $0.15 each, How many 20-cent stamps did Claire buy?

(1) Claire bought exactly 9 stamps

(2) The number of 20-cent stamps Claire bought was 1 more than the number of 15-cent stamps she bought.

My reason is: let # of 20-cent = x, # of 15-cent = y

From the question: 0.2x + 0.15y=1.6

From (1): x+y=9                           insufficient

From (2): x=y+1                            insufficient

(1) + (2) is sufficient, thus C

I picked C but the answer given is D. Can someone explain where I got it wrong? Or is this another misprint from the answer key? Thanks!

第三题：嗬嗬，ETS老鬼总是习惯这样。。。。

第六题：

给出二元一次不定方程：

0。15X+0.20y=1.60

得出两组正整数解：

X=4, y=5

x=8, y=2

因此答案（1）和答案（2）指的都是第一组解

ugh, shouldn't have tried to do math at night My brain is clearly not thinking!

Thanks...