Data Sufficiency

GMAT paper test Q

Given
.....Bio | !Bio
---------------------------
B | ?? | ?? | 18
---------------------------
G | ?? | ?? | ??
----------------------------
... | 26 | ?? | ?? = "TOTAL"

Need to figure out what "TOTAL" equals.

Note that TOTAL = 26 + !Bio
or TOTAL = 18 + GIRLS
so, if you can figure out how many students are not taking biology or how much students are girls, then you know the number in the class

1) 15 boys take biology
Bio | !Bio
---------------------------
B | 15 | 3 | 18
---------------------------
G | 11 | ?? | ??
----------------------------
... | 26 | ?? | ??

I could figure out certain other items, namely boys not taking biology and girls taking biology. But I still don't know the overall number of girls or those not taking biology.

Insufficient


2) Two times not taking bio = Girls

...... Bio | !Bio
---------------------------
B | ??? | ??? | 18
---------------------------
G | ??? | ??? | 2x
----------------------------
... | 26 | x | TOTAL

Don't know real numbers, but note that you do have to two equations and two unknowns (or you can look at it as two equations that have to equal each other)

26 + x = TOTAL
18 + 2x = TOTAL

=> 26 + x = 18 + 2x

At this point, I know that I can solve this to find x. Then I know the TOTAL.

Sufficient - Answer is (B)

For solution's sake, solving the equation that is set equal to each other, you can determine that x = 8, making TOTAL students = 34.

I just filled in the table and arrived at 26+x=18+2x which means X=8

26+8=34 is the total number of students

Answer B

A was insufficient.