IMO C is the ans
let initial amnt=x
at start=2x/3

s1)end=x/7
consumed=2x/3-x/7=11x/21

since we dnt know x its
insuff
s2)

2x/3=24
x=36
but we dnt wat was left after eating hence insuff

combining
11x/21=11*12/7
hence suff

bhumika.k.shah wrote:When Joanie began eating cereal, the box of cereal was 2/3 full. How many ounces of cereal did she end up eating?

1.)By the time she was done eating, the box was 1/7 full.
2.) When she first began eating, the box had 24 ounces of cereal.


I want some1 to explain me via plugging in #s....
and also tell me why is option A alone not sufficient

A. Say The box had 30 ounces of cereal. When Joanie started it had 20 and when she finished it had 30/7
now say if had only 15 ounces to start with, When Joanie started it had 10 and when she finished it had 15/7
so it is not sufficient to determine how much cereal the box had

It only say when she started the box had 2/3x and now it had only 1/7x; the amount eaten is (2/3-1/7)*x and x is not given in algebraic terms - NOT SUFF

B. Now when she started box had 24 ounces, which is 2/3 of the box size; the box size is 36... the ending position is not clear hence not SUFF to determine how much she ate

Combining - Box size 36, start 24 end 36/7 .. amount eaten (24-36/7) -- SuFF

C

for mixture ds problems such as this, i prefer taking the algebraic ruote shown by phoenix to the "take a value" method shown by ajith. It makes me me more confident. But, hey whatever works for you.

i would go one step further and assign another variable to what the questions is asking i.e. how many ounces did she end up eating

so, take x = number of ounces of whole cereal box
and y = ounces that Joanie ate

initially, 2x/3 ounces are there

Statement 1 -> 2x/3-y=x/7 -> y = x(2/3 - 1/7)
Two unknowns and only 1 equation, hence insufficient

Statement 2 -> x=24
This doesn't tell us anything about y(ounces eaten by Joanie), hence insufficient

Combining Statements 1 & 2 -> y=24(2/3 - 1/7) -> Sufficient as we are able to determine y (ounces eaten by Joanie)


Remember don't waste time getting the actual value of y. Just determine if sufficient or not.