The proportion needed of each starting percentage is the positive difference between the other two percentages.

Wt (10%) = 4-2 = 2

Wt( 2%) = 10-4= 6
cereal A to B = 2/6 = 1/3
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(10/100)A+(2/100)B = (4/100)(A+B)
6A =2B
=> A/B = 1/3

Answer is E.

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Excellent. Thank you mate. I liked the scale method lot better

10%------------|--------4%------2%

Distance between 10 and 4 is 6
Distance between 4 and 2 is 2.

Flip the numbers while forming the ratio. So 2:6 which is 1:3. Phew!

Hi All,

This is an example of a "Weighted Average" question. These types of prompts can be solved in a variety of ways - here's how you can use the Weighted Average Formula to answer the question:

We're told that two types of cereal....
1) A certain amount of Cereal A, which is 10% sugar by weight
2) A certain amount of Cereal B, which is 2% sugar by weight

....are mixed together to form a Cereal that is 4% sugar by weight.

We're asked for the ratio of Cereal A to Cereal B in the new cereal.

A = # of ounces of Cereal A
B = # of ounces of Cereal B

[.10(A) + .02(B)]/(A+B) = .04

.1A + .02B = .04A + .04B
.06A = .02B

6A = 2B

Since the question asks for A/B, we just have to do a little more math....

A/B = 2/6 = 1/3

Final Answer:

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Rich
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Simply set up an equation and solve for the answer.

Weights:
x+y=1
y=1-x
1=(1-x)+x

Solution equation with weights(note that x = part of cereal A/whole solution):
4=10x+2(1-x)
2=8x
1/4=x

As 1/4 of the solution is cereal A, the rest (3/4) must be cereal B.

1:3 is thus the answer.
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