GmatPrep 1

cramya wrote:Each of the students in a certain class received a single grade of P, F or I. What percent of students in the class were females ?

1. Of thse who received a P, 40% were females
2. Of those who received either F or I, 80% were males


Need to find F/M+F or f/m or m/f or m/m+f

Stmt I


.40P were females

Dont know any info about how many females received F or I, total strnegth of class etc...

INSUFF

Stmt I

.20 (F+I) were females

INSUFF(similar to above)

Together INSUFF (no idea how many females, males, total strength of class etc...)

Choose E)

are you posting this in the correct thread?

anyway, here's a response to it:

one way you could do it: number picking. just try different numbers of P's and I's/F's, and see whether the answer is invariant or whether it changes. if it changes at all, then the data are insufficient.

* let's try 100 p's and 100 f/i's
among the 100 p's, there are 60 males and 40 females.
among the 100 f/i's, there are 80 males and 20 females.
so 60 out of 200, or 30%, are female.

* let's try 1000 p's and 100 f/i's
among the 1000 p's, there are 600 males and 400 females.
among the 100 f/i's, there are 80 males and 20 females.
so 420 out of 1100 are female. this is a weird percentage, but it's clearly not 30% (which would be 330 out of 1100), so, insufficient.

--

you could also do it by realizing that this is a WEIGHTED AVERAGE of 40% (the percentage of p's that are female) and 20% (the percentage of f/i's that are female). like any other weighted average, this one depends on the relative quantities of its components (here, p's versus f/i's), quantities that are not given in either of the two statements.
conceptually, if there are huge numbers of p's and negligible numbers of f/i's, then the percentage of females will be very close to 40%. conversely, if there are huge numbers of f/i's and very few p's, then the percentage will be very close to 20%.

in fact, there's nothing prohibiting the consideration of the two most extreme cases possible:
* ALL grades are p's --> 40% female
* ALL grades are f/i's --> 20% female
these situations are both allowed under the given conditions, so, insufficient.