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Question

Alloy A is formed by mixing iron (Fe) and nickel (Ni) in the ratio 3:4, while alloy B is formed by mixing Fe and Ni in the ratio 9:5. If equal quantities of alloys A and B are melted together to form a new alloy C, what will be the ratio of Fe to Ni in the alloy C?

The correct answer is
15:13

Alloy Composition Calculation

The problem involves calculating the final ratio of Iron (Fe) to Nickel (Ni) in a new alloy (C) formed by melting equal quantities of two existing alloys (A and B) with different Fe:Ni ratios.

Alloy A Details

Alloy A is made of Fe and Ni in the ratio 3:4.

  • Fraction of Fe in Alloy A: $\frac{3}{3+4} = \frac{3}{7}$
  • Fraction of Ni in Alloy A: $\frac{4}{3+4} = \frac{4}{7}$

Alloy B Details

Alloy B is made of Fe and Ni in the ratio 9:5.

  • Fraction of Fe in Alloy B: $\frac{9}{9+5} = \frac{9}{14}$
  • Fraction of Ni in Alloy B: $\frac{5}{9+5} = \frac{5}{14}$

Mixing Equal Quantities

Assume we take an equal quantity, say 'Q' units, of both Alloy A and Alloy B.

Amount of Fe from Alloy A = $Q \times \frac{3}{7}$

Amount of Ni from Alloy A = $Q \times \frac{4}{7}$

Amount of Fe from Alloy B = $Q \times \frac{9}{14}$

Amount of Ni from Alloy B = $Q \times \frac{5}{14}$

New Alloy C Calculation

Alloy C is formed by melting these equal quantities together.

Total Fe in Alloy C = (Fe from A) + (Fe from B)

Total Fe = $Q \times \frac{3}{7} + Q \times \frac{9}{14} = Q \times (\frac{6}{14} + \frac{9}{14}) = Q \times \frac{15}{14}$

Total Ni in Alloy C = (Ni from A) + (Ni from B)

Total Ni = $Q \times \frac{4}{7} + Q \times \frac{5}{14} = Q \times (\frac{8}{14} + \frac{5}{14}) = Q \times \frac{13}{14}$

Final Ratio in Alloy C

The ratio of Fe to Ni in Alloy C is:

Ratio = (Total Fe) : (Total Ni)

Ratio = $(Q \times \frac{15}{14})$ : $(Q \times \frac{13}{14})$

Simplifying by canceling Q and multiplying by 14, we get:

Ratio = 15 : 13

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Important Questions from Mixture Problems (Notes)

  1. A has a container containing 60 litres of pure milk. He takes out 4 litres of milk and replaces it with the same quantity of water. He sells this mixture to B. B sells 30 litres of the mixture and added 5 litres of water in the remaining mixture. The ratio of milk to water in the remaining mixture is:
  2. How many liters of water should be added to a 30-liter mixture containing milk and water in the ratio 7:3 such that the resultant mixture has 40% water in it?
  3. A $595$ litre of mixture contains milk and water in the ratio $17:18$. How much milk must be added to the mixture so that it contains milk and water in the proportion of $3:2$?
  4. Suppose a tap mixes hot water and cold water in a ratio that depends linearly on the proportion of opening. Water out of the tap has temperature 40°C when the tap is half-open, and 30°C when it is three-fourths open. To get water at 50°C, the tap should be_______________.

  5. In 80 litres mixture of milk and water, the ratio of amount of milk to that of amount of water is 7 : 3. In order to make this ratio 2 : 1, how many litres of water should be added ?
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