28% of cars are tint and 18% of the old cars are tint. What

Question

28% of cars are tint and 18% of the old cars are tint. What is the ratio between number of new cars to number of old cars?

1). There are totally 250 cars

2). 40% of the new cars are tint.

Professor · Answer

C.

new = n
old = d
.4n+.18d= .28 of 250 ............................. i
n+d = 250 ............................................. ii

we can solve these equations...

conocieur · Answer

statement asks : new/old 

and we know from it : 28%*250 = 70 tint

(1) I think would not be enough, let see:

18% of old cars are tint. we can't do much with that.

(2) 
40% of new cars are tint
not enough

1 and 2

we would have two equations

L = old
N = new

L + N = 250
0.18L + 0.4N = 70

two equations, two variables
enough

I'll go with C

ywilfred · Answer

Total # of cars = c
Total # of old cars = o
Total # of new cars = n = c-o

Tinted: 0.28c
Tinted old cars = 0.18(o)

St1:
c = 250
But we do not know the breakdown between old and new cars. Insufficient.

St2:
Tinted new cars = 0.4(c-o). But we do not know exact figures for c and o. Insufficient.

Using St1 and St2:
c = 250
Tinted old car = 0.18(o)
Tinted new cars = 0.4(250-0)
Tinted cars = 70

We can calculate for o and thus c-o. Sufficient.

Ans C

BG · Answer

Hallo,Think it is B)
18/100 old+40/100 new=28/100 total
Total=new+old
Therefore, B is sufficient to answer the Q about the ratio
P.S. Good job Professor, simply you do not need 250

kumarece_2004 · Answer

Hi, I am not sure how come you got settled with Choice B.
The question in general ask the ration of new cars to old cars. But in the question and the two choices it deals with only tinted new and tinted old cards. So we cannot find the ratio of the new cars to old cards.
Might a slight change in the modification of the question will answer to CHOICE B.

Let me know if it is wrong!!!!!!!!!!

Professor · Answer

actually i wasn't confident about C. i know i was forgetting something but couldn't notw that new:old.

thanks BG. great work...

gmatmba · Answer

Lets assume x% of cars are old,
then (100-x)% cars are new.

from the question, (.28 * 100) cars are tinted
and (.18 * x) old cars are tinted

From 2:
0.4 * (100-x) new cars are tinted

So total tinted cars (in %) =>
{0.4 * (100-x)} + (.18 * x) = (.28 * 100)

Solving for x gives 1200/22

Ratio of old cars to new cars:
x/100-x) = 5/6

So, it appears that B could be sufficient. Please let me know if my calculations are incorrect anywhere.

giddi77 · Answer

Very late, but has to be B. The best approach is to express the required quantity with as few variables as possible as BG did! :good

Dilshod · Answer

The answer is B.
Old cars – o, New cars – n.
Statement 1 is insufficient: 250(o+n) cars, 70(o+n) of them are tint. 18 of n are tint, but to find the ratio of n to o, we should learn a connection between the numbers or proportion of o to n. St1 doesn’t give us that information.

Statement 2 is sufficient: (o+n)*0.28=o*0.40+n*0.18. From this we can find the ratio of o to n.

chiragr · Answer

Yep got B as answer 

BG, your approach is very good!

tl372 · Answer

I thought this was C at first but on closer examination, realized it was B. 

Great question!!

shahnandan · Answer

I solved it this way,

old=x
new=y

question's asking: y/x ?

whats given is : .28(x+y) cars are tinted out of which .18x are tinted (old cars)

stmt1, gives us (x+y) but we know the split so insuff

stmt2, gives us .40y (new cars)
combiningm with whats in the question you get
.18x+.4Y=.28(x+y) hence suff and B.

HongHu · Answer

Good job guys. This is a common type GMAT question. Almost guarenteed to appear in the test. Please remember the approach   and especially remember not to fall in the trap of thinking a total number is needed.

tl372 · Answer

B as well ..


It helps use visualize this using a chart with columns - Tint, no tint ...row - new, old. Then set the total = 100 (100%) and fill in the percentage information.

Doing this will show you more clearly that B is sufficient. As mentioned, # of total cars is not needed...we just need to know the ratio.

28% of cars are tint and 18% of the old cars are tint. What

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