Thread: how should i solve this question?

1. how should i solve this question?

The copper content of an alloy is 60%. If 1 kg of copper is added into the alloy, the copper content of the alloy will increase to 70%.
a. Find the original weight of the alloy.
b. Find the percentage change in the weight of the alloy.

I am learning about percentage change and found this question in my textbook. I don't know how to solve this question. Could you please help me? Thank you.

2. Re: how should i solve this question?

if n1 kg of a% alloy is mixed with n2 kg of b% alloy
then resultant alloy will have C%=(a*n1+b*n2)/(n1+n2)% alloy of n1+n2 kg.

let n kg of 60% alloy is taken
and 1 kg of 100%(pure copper) is taken
if mixed, we get C= 70% alloy.
i think you can do it now

3. Re: how should i solve this question?

Thanks for your information, but i don't really get it. I think for many days, still don't know how to finish the question. Can you show me how to set up the first step of the question?

4. Re: how should i solve this question?

Lets say the alloy is X kg.
Then the copper content is 0.6 X kg.
If one kg of copper is added to the alloy the the copper content is now 0.6X + 1.

The copper content should now be 70% of X+1.

0.6X + 1 / X + 1 = 0.7

Once you sove for X you will be able to find the percent change by calculating 1/X times 100

5. Re: how should i solve this question?

Thank you very much. I got it now.

6. Re: how should i solve this question?

Originally Posted by Veronica1999
0.6X + 1 / X + 1 = 0.7
There is no real solution to that, Veronica;
also no solution to 0.6X + 1 / (X + 1) = 0.7

Hamsters: you got what?!

7. Re: how should i solve this question?

Wilmer,
Are you not familiar with basic algebra?

0.6X + 1 = 0.7X + 0.7

0.1X = 0.3

x= 3

Therefore copper 1.8

2.8/4 = 70%

8. Re: how should i solve this question?

Originally Posted by Veronica1999
Wilmer,
Are you not familiar with basic algebra?
0.6X + 1 = 0.7X + 0.7
0.1X = 0.3
x= 3
Therefore copper 1.8
2.8/4 = 70%
AGREE, but ONLY if equation is: (0.6X + 1) / (X + 1) = 0.7

Your posted equation was: 0.6X + 1 / X + 1 = 0.7

Are you not familiar with basic order of operations?

Also not a good idea (confusing to student) to switch from X to x within same solution.

9. Re: how should i solve this question?

But if you understand the context of the problem
that kind of misunderstanding is less likely to happen....

10. Re: how should i solve this question?

There was NO misunderstanding on my part.
I did not attempt to solve the original problem.
I simply tried to solve YOUR equation, which has no real solution.

For you to call omission of brackets a misunderstanding....well, no comments.