Question 69843
<pre><font face = "lucida console" size = 5><b>Angus (was he a bull? <font face = "wingdings">J</font>) invested $18,000, part at 3%
and part at 5%.  If the total interest at the end of 
the year is $660, how much did he invest at each 
rate?

Let $x represent the first part, that is, the amount 
invested at 3%

Now use the formula for "the rest"<font color = "red">

<font face = "symbol">æ</font>The rest of   <font face = "symbol">ö</font>    <font face = "symbol">æ</font> The  <font face = "symbol">ö</font>   <font face = "symbol">æ</font> the <font face = "symbol">ö</font>
<font face = "symbol">ç</font>a total amount<font face = "symbol">÷</font>  = <font face = "symbol">ç</font>total <font face = "symbol">÷</font> - <font face = "symbol">ç</font>first<font face = "symbol">÷</font>
<font face = "symbol">ç</font>besides the   <font face = "symbol">÷</font>    <font face = "symbol">è</font>amount<font face = "symbol">ø</font>   <font face = "symbol">è</font> part<font face = "symbol">ø</font>
<font face = "symbol">è</font>first part    <font face = "symbol">ø</font>	
</font>
So the rest of the $18000 besides the $x
is = ($18000 - $x)

This amount (the rest besides the $x) was invested
at 5%. 

So we have x dollars invested at 3%
and (18000 - x) dollars invested at 5%

The interest on the x dollars is .03x dollars.

The interest on the (18000 - x) dollars is
.05(18000 - x)

We read:
>>...the total interest at the end of the year 
is $660...<<

|Interest |     |Interest|
|   on    |     |   on   |
|  the    |  +  |  the   |  =  $660 
|x dollars|     |18000-x |
                |dollars |
       
     .03x    +  .05(18000-x) = 660

Can you solve that? If not post again asking how.

You get x = $12000, which is the amount invested
at 3%.

To get the rest, which was invested at 5%, subtract
that $12000 from the total, $18000, and get $6000, 
the amount invested at 5%.

Edwin</pre>