BTGModeratorVI wrote: ↑Fri May 29, 2020 6:28 am
Zelma scored 90, 88, and 92 on 3 of the 6 mathematics tests that she took. What was her average (arithmetic mean) score on the 6 tests?
(1) Her average (arithmetic mean) score on 5 of the tests was 90.
(2) Her score on one of the tests was 91.
Answer:
E
Source: GMAT prep
Given: Zelma scored 90, 88, and 92 on 3 of the 6 mathematics tests
Target question: What was her average (arithmetic mean) score on the 6 tests?
When I SCAN the two statements, they both feel insufficient, AND I’m pretty sure I can identify some cases with conflicting answers to the
target question. So, I’m going to head straight to……
Statements 1 and 2 combined
Statement 1 tells us that the average score on 5 of the tests was 90.
Statement 2 tells us that her score on ONE of the tests was
91
Important: We cannot assume that the score of 91 (mentioned in statement 2) is DIFFERENT from the five scores mentioned in statement 1) goo
There are several sets of scores that satisfy BOTH statements. Here are two:
Case a: {
90,
88,
92,
91,
89, 90}.
Notice that the first 5 scores have an average of 90 (which satisfies the statement 1)
Also notice that
91 is among the first 5 scores (which satisfies statement 2)
This means the sixth score can have ANY value.
If the sixth score is 90 (as we have here), then
the average score is 90
Case b: {
90,
88,
92,
91,
89,
1,00,000}.
In this case,
the average score is much bigger than 90
Since we cannot answer the
target question with certainty, the combined statements are NOT SUFFICIENT
Answer: E
Cheers,
Brent
