marble ratios

[tim]

thanks!

[priyankapaul82]

Hi,

Isn't 6 White marbles in Bag A + 24 white marbles in Bag B a valid option?

With this I get 2 red marbles in Bag A and 6 red marbles in Bag B = 8 red marbles

Ans D

Not sure where I am going wrong :(

[krishnan.anju1987]

Bag A contains red, white and blue marbles such that the red to white marble ratio is 1:3 and the white to blue marble ratio is 2:3. Bag B contains red and white marbles in the ratio of 1:4. Together, the two bags contain 30 white marbles. How many red marbles could be in bag A?

a.1
b.3
c.4
d.6
e.8

I just don't seem to understand multiple ratios such as in this questions. Please help

Is this method logical?

The ratio of R:W:B balls in bag A is 2:6:9 and R:W in bag B is 1:4. Then, 6x+4y=30. Now consider the various answer options.

a)R(a)=1, not possible as it must be a multiple of 2 WRONG
2) Same reasoning as above does not let us take R(a)=3. WRONG
3) r(a)=4, implies actual number of balls of different colors in bag A is 4:12:18. This means bag B has 30-12=18 balls. 4y=18.18 is not divisible by 4 the number of white balls in B must be perfectly divisible by 4. WRONG
4) r(a)=6, thus the number of balls in A is 6:18:27. Thus, number of white balls in B is 30-18=12. 4y=12, which gives an integer value of Y. So possibly correct
5)R(A)=8, thus the ratio of balls in A becomes 8:24:36. Thus the white balls in B is 30-24=6. 4Y=6 does not give an integer value of Y and hence WRONG.

Thus the answer must be d.

[tim]

Priyanka, it sounds like you've got the correct approach, but 2 red marbles in A isn't an option, so you have to consider other possibilities. See esledge's post for more details..

Krishnan, your approach is totally correct..

[rustom.hakimiyan]

Hi,

In bag A, they give us a ratio of white to blue but that is nowhere to be found in the ask of the question stem.

I solved this by completely ignoring the W:B ratio in bag A, which meant that my R:W ratio in bag A was 1:3 and I didn't make it 2:6. Was this just a lucky guess on my end? Do I have to make the ratio in bag A equal to R 2, W 6, B 9?

[RonPurewal]

1:3 and 2:6 are exactly the same. (mathematically, fractions and ratios are equivalent, so these are the same just as 1/3 and 2/6 are the same fraction.)

and, yes, you can ignore the ratio of white to blue, since we don't care about the blue marbles.

[RonPurewal]

if the question were somewhat different, though, then you might have to take w:b into account.

for instance, say you were asked whether it's possible, with these ratios, to have 15 white marbles in bag A.
if all you used was r:w = 1:3, then you'd think "yes" (5 red, 15 white).
but, if it's also true that w:b = 2:3, it's no longer possible to have an odd number of white balls.