Question

qual dever ser o capital aplicado a uma taxa de juro simples de 25% a.a. para que em 6 meses renda R$ 425.00 de juro

Answer 1

Capital=?
taxa=25% ao ano,transformando em meses= 25/12=2,083% ao mês
tempo=6 meses
Juros=425

J=c.i.t
425=6x2,083/100
C=425/0,12498
c=3.400,54 é o capital aproximadamente

Answer 2

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

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