C)

how many were served double scoops? let number of people served double scoops = x, number of people served single scoops = y.
x=?

statement I: 60% were served double scoops. (x+y)*60/100 = x. or y=2x/3. insufficient.

statement II: total scoops = 120. number of single scoops + number of double scoops = 120. 2*x+y=120. insufficient.

together, 2x+y=120 and y=2x/3, so x = 45. 45 people were served double scoops.

Total # of guests = n

From (1), 60%*n got double scoops, but we have no value for n. So (1) is not sufficient.

From (2), we have no useful information here. (2) is not sufficient.

Using both (1) and (2), we can equate 60%*n*2 + 40%*n*1 = 120 and solve for n.

Ans: C

X is single scoop, Y is double scoop

X + 2Y = 120
Y/X + Y = 60/100
100Y = 60X + 60Y
40Y = 60X
Y = 3/2X
X = 30
Y = 45
Answer: C

Assume number of people = x

St1:
0.6x --> double scoops
0.4x --> single scoop

Insufficient as we cannot solve for x

St2:
Insufficient as we cannot break down the number of people who were served double scoops and the number of people who were served single scoops.

St1 and St2:
0.6x(2) + 0.4x = 120

Sufficient as we can solve for x, and thus 0.6x.

Ans C

At a certain picnic, each of the guests was served either a single scoop or a double scoop of ice cream. How many of the guests were served a double scoop of ice cream?
(1) At the picnic, 60 percent of the guests were served a double scoop of ice cream.
(2) A total of 120 scoops of ice cream were served to all the guests at the picnic


(1) We dont know total # of guests, so not sufficient

(2) not sufficient either

Taking both together:

Let there be x guests,
(0.6x*2) + 0.4x = 120
Solving, x=75 guests

Hence C

assume x= total number of guests

x*0.6*2 (2 scoops)+ x*0.4* 1(1 scoop) =120
x 1.6=120
x= 75

At a certain picnic, each of the guests was served either a single scoop or a double scoop of ice cream. How many of the guests were served a double scoop of ice cream?

(1) At the picnic, 60 percent of the guests were served a double scoop of ice cream.

(2) A total of 120 scoops of ice cream were served to all the guests at the picnic.

from 1.......insuff
from2
insuff

both

120 = 1.2x+0.4x.........suff..........c

x - single scoop, y - double scoops. the question asks about y.

1: insufficient, only ratio y/(x+y) given
2: insufficient (x+2*y = 120, can't calculate y)

1+2: sufficient
y = 0.6*(x+y)
x+2*y = 120 -> sufficient to calculate y -> C

hmm.pretty surprised..I somehow remember seeing a diff. solution somewhere..anyways this is an OG question so the OA C must be correct.
IMO I got B.
Single scoop=x
Double scoop=x+x=2x
This makes stmt 2: 3x=120 making it suff..
HUh>??

I would like to know,whether the number of scoops can be divided in a way other than
Single=40
Double=40

That makes the total scoops equal to 120

IMO E

The Q doesn't say whether any quest has been serverd 2 scoops of double scoop or single scoop.

At a certain picnic, each of the guests was served either a single scoop or a double scoop ice-cream. How many of the guests were served a double scoop of ice-cream?

(1) At the picnic, 60 percent of the guests were served a double scoop of ice-cream --> \(\frac{x}{y}=\frac{4}{6}=\frac{2}{3}\), where \(x\) is the # of people served single scoop and \(y\) the # of people served double scoop. Clearly insufficient to calculate single numerical value of \(y\).

(2) A total of 120 scoops of ice-cream were served to all the guests at the picnic --> \(1*x+2*y=120\). Again not sufficient.

(1)+(2) \(x=\frac{2}{3}y\) and \(x+2y=120\) --> \(\frac{2}{3}y+2y=120\) --> \(y=45\). Sufficient.

Answer: C.
_________________

At a certain picnic, each of the guests was served either a single scoop or a double scoop ice-cream. How many of the guests were served a double scoop of ice-cream?

All guests = guests served a single scoop ice-cream + guests served a double scoop ice-cream

1) At the picnic, 60 percent of the guests were served a double scoop of ice-cream.

It is just percent but we need numbers. Insufficient.

2) A total of 120 scoops of ice-cream were served to all the guests at the picnic.

So, we know that All guests = 120 but it still insufficient.

1)&2) We know from first statement that the number of guests served a double scoop of ice-cream is 60% of the number of all guests. Therefore, we take 120 from second statement and get 0.6*120 = 72.

Hope it helps
_________________

Walker I think statement (2) is saying that "120 scoops of ice-cream were served" not that the total # of guests were 120. Am I interpreting the statement in the wrong way?
_________________

@Bunuel: Thanks man, I found your answer explanatory.

i found i was doing some stupid mistakes while solving this

@ walker: i have a Question, how can we assume total # of Guests = total # of scoops?

st 1 indicates total scoops of ice cream and its different from total number of guests

You are right, guys, my bad
_________________

And yet, you got away with a 50 on Quant?? Man, this is unfair!!!!

{J/K}

Yeah, I know. Q51 would be better
By the way, one very silly mistake on my real GMAT led me to Q50.... So, be very careful....
_________________