Question

Qual deve ser o capital aplicado a uma taxa de juro simpels de 25%a.a. para que em 6 meses renda R$ 425,00 de juro ?

Answer 1

Taxa de juros simples:

25% aa em 6 meses = 12,5% (meio ano)

x . 12,5/100 = 425
12,5x = 425 . 100
x = 42500/12,5
x = 3400

Deve-se aplicar um capital de R$ 3400,00

=)

Answer 2

$\sf\large \boxed{\boxed{\tt J = C \cdot i \cdot t}}$

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$\sf \displaystyle 425\:=\:C\:\cdot 0,\:25\:\cdot \left(\frac{1}{2}\right)\\\\\\\sf \boxed{\star \sf \ {Troque \:os \:lados} }\\\\\\\sf C\cdot \:0.25\left(\frac{1}{2}\right)=425\\\\\\\sf C\frac{0.25}{2}=425\\\\\\\sf 2C\frac{0.25}{2}=425\cdot \:2\\\\\\\sf 0.25C=850\\\\\\\sf \frac{0.25C}{0.25}=\frac{850}{0.25}\\\\\\\\\large \to \boxeed{\boxed{\sf C=3400}}$