Math test

There are 2 bars of copper-silver alloy; one piece has 3 parts of copper to 4 parts of silver and another has 2 parts of copper to 5 parts of silver. If both bars are melted into 11pounds of bar with the final copper to silver ratio of 4:7. What was the weight of the first bar?

1. 1 kg
2. 3 kg
3. 5 kg
4. 6 kg
5. 7 kg

Answer: D

Explanation:

We can form equation to solve this question.

“x” is the weight of first bar, then (11-x) is the weight of second bar.

\frac{3}{7}+\frac{2}{7}(11-x)=\frac{4}{11}(11)

1. \frac{1}{100}

Solving it we get,

x = 6

1. 101​
2. \frac{1}{100}​

Hence the answer is D.

y = \left(x+y\right)^2=\frac{1}{100}

X