First theory (from
MGMAT)
Concrete valueIf a Data Sufficiency question asks for the concrete value of one element of a ratio, you will need
BOTH the concrete value of another element of the ratio AND the relative value of two elements
of the ratio.
Relative valueIf a Data Sufficiency question asks for the relative value of two pieces of a ratio, ANY statement
that gives the relative value of ANY two pieces of the ratio will be sufficient.
We can solve this question using
ratiosD= # of double-Scoop portions served
T= # Total portions served
(1) At the picnic, 60 percent of the guests were served a double scoop of ice cream.
This statement tells us that the ratio of D/T = 3/5 Not Sufficient (See explanation above - we are asked to find the concrete Value)
(2) A total of 120 scoops of ice cream were served to all the guests at the picnic.
Not sufficient because we need add. a ratio od D/T to answer this question
(1+2) D/S = 3/5 so we have 3x+5x = 120
X = 15 --> D=3*15 =45 (C) Correct, can be calculated, BUT if you know the theory you don't need to calculate by DS Questions, it's enoough to know whether it can be calculated or not.
Hope this helps