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HEPENNYPECKER, IF ANY OF YOU CAN MAKE ME UNDERSTAND WHERE AM I GOING WRONG
IF THERE'S AN ALLOY OF 9 GMS THEN A WILL HAVE 8GMS - COPPER AND 1GM - ZINC
B WILL HAVE 2GMS - COPPER AND 7 GMS - ZINC
RATIO OF MIXTURE (WHEN MIXED) A:B = COPPER:ZINC, IF I AM TAKING MIXTURE A:B IN 2:1
THEN TWICE OF A = 2(8:1) SIMILARLY 3:1 IS ALSO SATISFIED AS 3(8:1)
+ 1B = (2:7) (2:7)
= 18:9 = 26:10
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Given: There are two alloys, A and B, of copper and zinc. The ratio (by weight) of copper and zinc in alloy A is 8 : 1 and that in alloy B is 2 : 7. It is found that, if alloy A and alloy B are mixed in a certain ratio, the weights of copper and zinc in the resultant alloy are also in that ratio.

Asked: What is that ratio?

Let the ratio be x.

Copper = 8x + 2
Zinc = x + 7

(8x+2)/(x+7) = x
8x + 2 = x^2 + 7x
x^2 - x - 2 = 0
(x-2)(x+1) = 0
x = 2

IMO D
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Let c be copper and let z be zinc.

Alloy A has 8c and 1z and Alloy B has 2c and 7z

Multiply the given ratio with the copper and zinc values of A and B and the correct answer will end up as the ratio itself.

Ans is D because

2/3*(8c+z) + 1/3*(2c+7z) gives (18c + 9z)/3 = 6c + 3z = 3(2c + z) which is the ratio (2:1) itself
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HEPENNYPECKER, IF ANY OF YOU CAN MAKE ME UNDERSTAND WHERE AM I GOING WRONG
IF THERE'S AN ALLOY OF 9 GMS THEN A WILL HAVE 8GMS - COPPER AND 1GM - ZINC
B WILL HAVE 2GMS - COPPER AND 7 GMS - ZINC
RATIO OF MIXTURE (WHEN MIXED) A:B = COPPER:ZINC, IF I AM TAKING MIXTURE A:B IN 2:1
THEN TWICE OF A = 2(8:1) SIMILARLY 3:1 IS ALSO SATISFIED AS 3(8:1)
+ 1B = (2:7) (2:7)
= 18:9 = 26:10

Please check your last step, the two ratios aren't equal, i.e. 18:9 != 26:10
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HEPENNYPECKER
Let, the ratio is K:1

SO, Copper : Zinc = 8k+2 : k+7
Now,
8k+2/k+7= k/1

solve for k, k=2

so the ratio is k:1=2:1
Why does the ratio have to be k:1 here? Doesn't it have to be x:y? (That makes the overall calculations complicated though)
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