In article <firstname.lastname@example.org>, "lionel vulliemin" <email@example.com> wrote:
>Good morning, I come swiss, and hoe that someone could help me with this >problem: >we have 2 summ put in an account for a total of 20.000 $ . >the first have t%, and give 1.080 $ interest par year. >the second have (t+1)% , and it give 800 $ par year. >find the two capital ? >I don't now how to find the result ! on the book, it's writing the first one >have a capital of 12.000$, and the second have 8.000$...... could you give >me the way to find these 2 capitals. >Thank you very much
Firstly, check the book answer; if you can't do that then either the book is wrong (possible but unlikely) or you don't adequately understand the problem: $12000 * t/100 = $1080, so t must = 9; then $ 8000 * (9+1)/100 should = 800, which it does. So, the book answer checks.
Now, setting up the equations, let x the capital amount at the t% rate; then (20000 - x) is the amount at the (t+1)% rate, so x * t/100 = 1080; and (20000 - x) * (t+1)/100 = 800. This is 2 equations in 2 unknowns, which you should be able to reduce to 1 equation in 1 unknown by substitution (by solving the first equation for x or for t -- your choice).
Then solve that final equation (which will be a quadratic) for its 1 unknown, and use that value in the first equation to calculate the other unknown.
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